A call to action to advance patient-focused and decentralized clinical trials

This commentary is a call to action for a concerted commitment and effort to transform clinical trials and enable people with cancer to participate in clinical trials closer to home. Three key strategies are identified to address major barriers: confront challenges with the interpretation of US Food and Drug Administration Form 1572 requirements (Statement of Investigator); broaden acceptance of local laboratories and imaging centers; and invest in the creation of effective, sustainable partnerships between research centers and local providers.

Afamitresgene autoleucel for advanced synovial sarcoma and myxoid round cell liposarcoma (SPEARHEAD-1): an international, open-label, phase 2 trial

BACKGROUND

Afamitresgene autoleucel (afami-cel) showed acceptable safety and promising efficacy in a phase 1 trial (NCT03132922). The aim of this study was to further evaluate the efficacy of afami-cel for the treatment of patients with HLA-A*02 and MAGE-A4-expressing advanced synovial sarcoma or myxoid round cell liposarcoma.

METHODS

SPEARHEAD-1 was an open-label, non-randomised, phase 2 trial done across 23 sites in Canada, the USA, and Europe. The trial included three cohorts, of which the main investigational cohort (cohort 1) is reported here. Cohort 1 included patients with HLA-A*02, aged 16-75 years, with metastatic or unresectable synovial sarcoma or myxoid round cell liposarcoma (confirmed by cytogenetics) expressing MAGE-A4, and who had received at least one previous line of anthracycline-containing or ifosfamide-containing chemotherapy. Patients received a single intravenous dose of afami-cel (transduced dose range 1·0 × 109-10·0 × 109 T cells) after lymphodepletion. The primary endpoint was overall response rate in cohort 1, assessed by a masked independent review committee using Response Evaluation Criteria in Solid Tumours (version 1.1) in the modified intention-to-treat population (all patients who received afami-cel). Adverse events, including those of special interest (cytokine release syndrome, prolonged cytopenia, and neurotoxicity), were monitored and are reported for the modified intention-to-treat population. This trial is registered at ClinicalTrials.gov, NCT04044768; recruitment is closed and follow-up is ongoing for cohorts 1 and 2, and recruitment is open for cohort 3.

FINDINGS

Between Dec 17, 2019, and July 27, 2021, 52 patients with cytogenetically confirmed synovial sarcoma (n=44) and myxoid round cell liposarcoma (n=8) were enrolled and received afami-cel in cohort 1. Patients were heavily pre-treated (median three [IQR two to four] previous lines of systemic therapy). Median follow-up time was 32·6 months (IQR 29·4-36·1). Overall response rate was 37% (19 of 52; 95% CI 24-51) overall, 39% (17 of 44; 24-55) for patients with synovial sarcoma, and 25% (two of eight; 3-65) for patients with myxoid round cell liposarcoma. Cytokine release syndrome occurred in 37 (71%) of 52 of patients (one grade 3 event). Cytopenias were the most common grade 3 or worse adverse events (lymphopenia in 50 [96%], neutropenia 44 [85%], leukopenia 42 [81%] of 52 patients). No treatment-related deaths occurred.

INTERPRETATION

Afami-cel treatment resulted in durable responses in heavily pre-treated patients with HLA-A*02 and MAGE-A4-expressing synovial sarcoma. This study shows that T-cell receptor therapy can be used to effectively target solid tumours and provides rationale to expand this approach to other solid malignancies.

FUNDING

Adaptimmune.

ATRX guards against aberrant differentiation in mesenchymal progenitor cells

Alterations in the tumor suppressor ATRX are recurrently observed in mesenchymal neoplasms. ATRX has multiple epigenetic functions including heterochromatin formation and maintenance and regulation of transcription through modulation of chromatin accessibility. Here, we show in murine mesenchymal progenitor cells (MPCs) that Atrx deficiency aberrantly activated mesenchymal differentiation programs. This includes adipogenic pathways where ATRX loss induced expression of adipogenic transcription factors and enhanced adipogenic differentiation in response to differentiation stimuli. These changes are linked to loss of heterochromatin near mesenchymal lineage genes together with increased chromatin accessibility and gains of active chromatin marks. We additionally observed depletion of H3K9me3 at transposable elements, which are derepressed including near mesenchymal genes where they could serve as regulatory elements. Finally, we demonstrated that loss of ATRX in a mesenchymal malignancy, undifferentiated pleomorphic sarcoma, results in similar epigenetic disruption and de-repression of transposable elements. Together, our results reveal a role for ATRX in maintaining epigenetic states and transcriptional repression in mesenchymal progenitors and tumor cells and in preventing aberrant differentiation in the progenitor context.

The MOTION study: a randomized, phase III study of vimseltinib for the treatment of tenosynovial giant cell tumor

Tenosynovial giant cell tumor (TGCT) is a rare, locally aggressive neoplasm that occurs in the synovium of joints, bursae, or tendon sheaths and is caused by upregulation of the CSF1 gene. Vimseltinib is an oral switch-control tyrosine kinase inhibitor specifically designed to selectively and potently inhibit the CSF1 receptor. Here, we describe the rationale and design for the phase III MOTION trial (NCT05059262), which aims to evaluate the efficacy and safety of vimseltinib in participants with TGCT not amenable to surgical resection. In part 1, participants are randomized to receive vimseltinib 30 mg twice weekly or matching placebo for ≤24 weeks. Part 2 is a long-term treatment phase in which participants will receive open-label vimseltinib.

Sarcoma microenvironment cell states and ecosystems are associated with prognosis and predict response to immunotherapy

Characterization of the diverse malignant and stromal cell states that make up soft tissue sarcomas and their correlation with patient outcomes has proven difficult using fixed clinical specimens. Here, we employed EcoTyper, a machine-learning framework, to identify the fundamental cell states and cellular ecosystems that make up sarcomas on a large scale using bulk transcriptomes with clinical annotations. We identified and validated 23 sarcoma-specific, transcriptionally defined cell states, many of which were highly prognostic of patient outcomes across independent datasets. We discovered three conserved cellular communities or ecotypes associated with underlying genomic alterations and distinct clinical outcomes. We show that one ecotype defined by tumor-associated macrophages and epithelial-like malignant cells predicts response to immune-checkpoint inhibition but not chemotherapy and validate our findings in an independent cohort. Our results may enable identification of patients with soft tissue sarcomas who could benefit from immunotherapy and help develop new therapeutic strategies.

The patient perspective on sirolimus for epithelioid hemangioendothelioma (EHE): results of a community survey highlighting the importance of equitable access to treatments

Background

Epithelioid hemangioendothelioma (EHE) is an ultra-rare, vascular sarcoma with clinical presentation ranging from an indolent to an aggressive form. Over 50% of patients present with metastatic disease, requiring systemic therapy, although no systemic therapies are specifically approved for EHE. Retrospective evidence supports the activity of mTOR inhibitors (e.g. sirolimus), although available only off-label. EHE patients and advocates are therefore working to support approval of effective treatments by collecting data on patient perspectives and experiences.

Materials and methods

In February 2023, the EHE Rare Cancer Charity (UK) and The EHE Foundation (US), with other advocates, conducted a survey of perspectives and experiences of EHE patients regarding the use and accessibility of sirolimus. The survey consisted of 20 questions designed for individuals undergoing treatment, those who had been treated, or had never been treated with the drug. Widely promoted within the patient community, the online survey categorized patients into three cohorts for the analysis: liver transplant patients, non-transplant patients who had ever taken sirolimus and sirolimus-naïve non-transplant patients.

Results

The survey evaluated data from 129 patient responses from 21 countries, mostly from USA, UK, Australia, and Canada (70%). The liver transplant, sirolimus and non-sirolimus cohorts were 16%, 25% and 59%, respectively. In the sirolimus group 66% reported treatment durations exceeding one year, with 16% exceeding five years, indicating the drug's efficacy. In the non-sirolimus group, the drug was not available for 42% and for 11% sirolimus was available but not selected for treatment because of its off-label status. Overall, 87% of all patients across all cohorts expressed the importance of the drug's availability as hugely or very important.

Conclusion

The survey responses highlight the activity of sirolimus for EHE and the importance of securing a label extension for the drug delivering equitable access to this treatment for patients.

Therapy-Induced Senescence Contributes to the Efficacy of Abemaciclib in Patients with Dedifferentiated Liposarcoma

PURPOSE

We conducted research on CDK4/6 inhibitors (CDK4/6i) simultaneously in the preclinical and clinical spaces to gain a deeper understanding of how senescence influences tumor growth in humans.

PATIENTS AND METHODS

We coordinated a first-in-kind phase II clinical trial of the CDK4/6i abemaciclib for patients with progressive dedifferentiated liposarcoma (DDLS) with cellular studies interrogating the molecular basis of geroconversion.

RESULTS

Thirty patients with progressing DDLS enrolled and were treated with 200 mg of abemaciclib twice daily. The median progression-free survival was 33 weeks at the time of the data lock, with 23 of 30 progression-free at 12 weeks (76.7%, two-sided 95% CI, 57.7%-90.1%). No new safety signals were identified. Concurrent preclinical work in liposarcoma cell lines identified ANGPTL4 as a necessary late regulator of geroconversion, the pathway from reversible cell-cycle exit to a stably arrested inflammation-provoking senescent cell. Using this insight, we were able to identify patients in which abemaciclib induced tumor cell senescence. Senescence correlated with increased leukocyte infiltration, primarily CD4-positive cells, within a month of therapy. However, those individuals with both senescence and increased TILs were also more likely to acquire resistance later in therapy. These suggest that combining senolytics with abemaciclib in a subset of patients may improve the duration of response.

CONCLUSIONS

Abemaciclib was well tolerated and showed promising activity in DDLS. The discovery of ANGPTL4 as a late regulator of geroconversion helped to define how CDK4/6i-induced cellular senescence modulates the immune tumor microenvironment and contributes to both positive and negative clinical outcomes. See related commentary by Weiss et al., p. 649.

Challenges and Solutions to Support Oncology Professionals Serving Underserved Populations With Cancer in the United States: Results From the ASCO Serving the Underserved Task Force

PURPOSE

Little data exist regarding approaches to support oncology professionals who deliver cancer care for underserved populations. In response, ASCO developed the Serving the Underserved Task Force to learn from and support oncology professionals serving underserved populations.

METHODS

The Task Force developed a 28-question survey to assess oncology professionals' experiences and strategies to support their work caring for underserved populations. The survey was deployed via an online link to 600 oncology professionals and assessed respondent and patient demographic characteristics, clinic-based processes to coordinate health-related social services, and strategies for professional society support and engagement. We used chi-square tests to evaluate whether there were associations between percent full-time equivalent (FTE) effort serving underserved populations (<50% FTE v ≥50% FTE) with responses.

RESULTS

Of 462 respondents who completed the survey (77% response rate), 79 (17.1%) were Asian; 30 (6.5%) Black; 43 (9.3%) Hispanic or Latino/Latina; and 277 (60%) White. The majority (n = 366, 79.2%) had a medical doctor degree (MD). A total of 174 (37.7%) had <25% FTE, 151 (32.7%) had 25%-50% FTE, and 121 (26.2%) had ≥50% FTE effort serving underserved populations. Most best guessed patients' sociodemographic characteristics (n = 388; 84%), while 42 (9.2%) used data collected by the clinic. Social workers coordinated most health-related social services. However, in clinical settings with high proportions of underserved patients, there was greater reliance on nonclinical personnel, such as navigators (odds ratio [OR], 2.15 [95% CI, 1.07 to 4.33]) or no individual (OR, 2.55 [95% CI, 1.14 to 5.72]) for addressing mental health needs and greater reliance on physicians or advance practice practitioners (OR, 2.54 [95% CI, 1.11 to 5.81]) or no individual (OR, 1.91 [95% CI, 1.09 to 3.35]) for addressing childcare or eldercare needs compared with social workers. Prioritization of solutions, which did not differ by FTE effort serving underserved populations, included a return-on-investment model to support personnel, integrated health-related social needs screening, and collaboration with the professional society on advocacy and policy.

CONCLUSION

The findings highlight crucial strategies that professional societies can implement to support oncology clinicians serving underserved populations with cancer.

Chromoplexy is a frequent early clonal event in EWSR1-rearranged round cell sarcomas that can be detected using clinically validated targeted sequencing panels

Chromoplexy is a phenomenon defined by large-scale chromosomal chained rearrangements. A previous study observed chromoplectic events in a subset of Ewing sarcomas (ES), which was linked to an increased relapse rate. Chromoplexy analysis could potentially facilitate patient risk stratification, particularly if it could be detected with clinically applied targeted next-generation sequencing (NGS) panels. Using DELLY, a structural variant (SV) calling algorithm that is part of the MSK-IMPACT pipeline, we characterized the spectrum of SVs in EWSR1-fused round cell sarcomas, including 173 ES and 104 desmoplastic small round cell tumors (DSRCT), to detect chromoplexy and evaluate its association with clinical and genomic features. Chromoplectic events were detected in 31% of the ES cases and 19% of the DSRCT cases. EWSR1 involvement accounted for 76-93% of these events, being rearranged with diverse non-canonical gene partners across the genome, involving mainly translocations but also intrachromosomal deletions and inversions. A major breakpoint cluster was located on EWSR1 exons 8-13. In a subset of cases, the SVs disrupted adjacent loci, forming deletion bridges. Longitudinal sequencing and breakpoint allele fraction analysis showed that chromoplexy is an early event that remains detectable throughout disease progression and likely develops simultaneously with the driver fusion. The presence of chromoplexy was validated in an external ES patient cohort with whole exome sequencing. Chromoplexy was significantly more likely to be present in cases that were metastatic at presentation. Together, this study identifies chromoplexy as a frequent genomic alteration in diverse EWSR1-rearranged tumors that can be captured by targeted NGS panels.

Incremental Utility of First-Pass Perfusion CMR for Prognostic Risk Stratification of Cancer-Associated Cardiac Masses

BACKGROUND

Cardiac magnetic resonance (CMR) differentiates cardiac metastasis (CMET) and cardiac thrombus (CTHR) based on tissue characteristics stemming from vascularity on late gadolinium enhancement (LGE). Perfusion CMR can assess magnitude of vascularity; utility for cardiac masses (CMASS) is unknown.

OBJECTIVES

This study sought to determine if perfusion CMR provides diagnostic and prognostic utility for CMASS beyond binary differentiation of CMET and CTHR.

METHODS

The population comprised adult cancer patients with CMASS on CMR; CMET and CTHR were defined using LGE-CMR: CMASS+ patients were matched to CMASS- control subjects for cancer type/stage. First-pass perfusion CMR was interpreted visually and semiquantitatively for CMASS vascularity, including contrast enhancement ratio (CER) (plateau vs baseline) and contrast uptake rate (CUR) (slope). Follow-up was performed for all-cause mortality.

RESULTS

A total of 462 cancer patients were studied, including patients with (CMET = 173, CTHR = 69) and without CMASS on LGE-CMR. On perfusion CMR, CER and CUR were higher within CMET vs CTHR (P < 0.001); CUR yielded better performance (AUC: 0.89-0.93) than CER (AUC: 0.66-0.72) (both P < 0.001) to differentiate LGE-CMR-evidenced CMET and CTHR, although both CUR (P = 0.10) and CER (P = 0.01) typically misclassified CMET with minimal enhancement. During follow-up, mortality among CMET patients was high but variable; 47% of patients were alive 1 year post-CMR. Patients with semiquantitative perfusion CMR-evidenced CMET had higher mortality than control subjects (HR: 1.42 [95% CI: 1.06-1.90]; P = 0.02), paralleling visual perfusion CMR (HR: 1.47 [95% CI: 1.12-1.94]; P = 0.006) and LGE-CMR (HR: 1.52 [95% CI: 1.16-2.00]; P = 0.003). Among patients with CMET on LGE-CMR, mortality was highest among patients (P = 0.002) with lesions in the bottom perfusion (CER) tertile, corresponding to low vascularity. Among CMET and cancer-matched control subjects, mortality was equivalent (P = NS) among patients with lesions in the upper CER tertile (corresponding to higher lesion vascularity). Conversely, patients with CMET in the middle (P = 0.03) and lowest (lowest vascularity) (P = 0.001) CER tertiles had increased mortality.

CONCLUSIONS

Perfusion CMR yields prognostic utility that complements LGE-CMR: Among cancer patients with LGE-CMR defined CMET, mortality increases in proportion to magnitude of lesion hypoperfusion.

Subclonal Somatic Copy-Number Alterations Emerge and Dominate in Recurrent Osteosarcoma

Multiple large-scale genomic profiling efforts have been undertaken in osteosarcoma to define the genomic drivers of tumorigenesis, therapeutic response, and disease recurrence. The spatial and temporal intratumor heterogeneity could also play a role in promoting tumor growth and treatment resistance. We conducted longitudinal whole-genome sequencing of 37 tumor samples from 8 patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and a metastatic or relapse site. Subclonal copy-number alterations were identified in all patients except one. In 5 patients, subclones from the primary tumor emerged and dominated at subsequent relapses. MYC gain/amplification was enriched in the treatment-resistant clones in 6 of 7 patients with multiple clones. Amplifications in other potential driver genes, such as CCNE1, RAD21, VEGFA, and IGF1R, were also observed in the resistant copy-number clones. A chromosomal duplication timing analysis revealed that complex genomic rearrangements typically occurred prior to diagnosis, supporting a macroevolutionary model of evolution, where a large number of genomic aberrations are acquired over a short period of time followed by clonal selection, as opposed to ongoing evolution. A mutational signature analysis of recurrent tumors revealed that homologous repair deficiency (HRD)-related SBS3 increases at each time point in patients with recurrent disease, suggesting that HRD continues to be an active mutagenic process after diagnosis. Overall, by examining the clonal relationships between temporally and spatially separated samples from patients with relapsed/refractory osteosarcoma, this study sheds light on the intratumor heterogeneity and potential drivers of treatment resistance in this disease.

SIGNIFICANCE

The chemoresistant population in recurrent osteosarcoma is subclonal at diagnosis, emerges at the time of primary resection due to selective pressure from neoadjuvant chemotherapy, and is characterized by unique oncogenic amplifications.

Immune-related Adverse Events after Immune Checkpoint Blockade-based Therapy Are Associated with Improved Survival in Advanced Sarcomas

The association between immune-related AEs (irAE) and outcome in patients with sarcoma is not known. We retrospectively reviewed a cohort of patients with advanced sarcoma treated with immune checkpoint blockade (ICB)-based therapy. Association of irAEs with survival was assessed using a Cox regression model that incorporated irAE occurrence as a time-dependent covariate. Tumor samples with available RNA sequencing data were stratified by presence of an irAE to identify patterns of differential gene expression. A total of 131 patients were included. Forty-two (32%) had at least one irAE of any grade and 16 (12%) had at least one grade ≥ 3 irAE. The most common irAEs were hypothyroidism (8.3%), arthralgias (5.3%), pneumonitis (4.6%), allergic reaction (3.8%), and elevated transaminases (3.8%). Median progression-free survival (PFS) and overall survival (OS) from the time of study entry were 11.4 [95% confidence interval (CI), 10.7-15.0) and 74.6 weeks (CI, 44.9-89.7), respectively. On Cox analysis adjusting for clinical covariates that were significant in the univariate setting, the HR for an irAE (HR, 0.662; CI, 0.421-1.041) approached, but did not reach statistical significance for PFS (P = 0.074). Patients had a significantly lower HR for OS (HR, 0.443; CI, 0.246-0.798; P = 0.007) compared with those without or before an irAE. Gene expression profiling on baseline tumor samples found that patients who had an irAE had higher numbers of tumor-infiltrating dendritic cells, CD8+ T cells, and regulatory T cells as well as upregulation of immune and inflammatory pathways.

SIGNIFICANCE

irAE after ICB therapy was associated with an improved OS; it also approached statistical significance for improved PFS. Patients who had an irAE were more likely to have an inflamed tumor microenvironment at baseline.

Novel Genomic Risk Stratification Model for Primary Gastrointestinal Stromal Tumors (GIST) in the Adjuvant Therapy Era

PURPOSE

Traditional risk stratification schemes in gastrointestinal stromal tumors (GIST) were defined in the pre-imatinib era and rely solely on clinicopathologic metrics. We hypothesize that genomic-based risk stratification is prognostically relevant in the current era of tyrosine kinase inhibitor (TKI) therapeutics.

EXPERIMENTAL DESIGN

Comprehensive mutational and copy-number profiling using MSK-IMPACT was performed. We integrated clinicopathologic and genomic parameters and utilized an elastic-net penalized Cox proportional hazards machine learning model for outcome risk stratification.

RESULTS

A 3-tier genomic risk stratification model for recurrence-free survival (RFS) in 152 primary localized gastric and 80 small bowel GISTs was proposed. Gastric GISTs were classified as high risk if chr1p deletion or SDHB loss was present, and intermediate risk if chr14q deletion was present or KIT exon 11 mutation was absent. Small bowel GISTs were classified as high risk if MAX/MGA/MYC, CDKN2A, or RB1 alterations were present, and intermediate risk if chr1p deletion or chr5q amplification was present. Compared with conventional risk stratification, genomic risk stratification both upgrades and downgrades, suggesting that conventional risk stratification may underestimate or overtreat some high-risk and low-risk patients, respectively. Longitudinal sequencing detected most KIT-independent genomic alterations at baseline. Subanalysis in 26 SDH-deficient GISTs revealed that presence of TP53 mutations or chr1q amplifications portends worse RFS and disease-free survival.

CONCLUSIONS

We developed a novel, next-generation genomic risk stratification model for primary gastric and small bowel GISTs, complementing traditional clinicopathologic models. Future independent validation of our model in external cohorts is essential.

An interpretable AI model for recurrence prediction after surgery in gastrointestinal stromal tumour: an observational cohort study

Background

There are several models that predict the risk of recurrence following resection of localised, primary gastrointestinal stromal tumour (GIST). However, assessment of calibration is not always feasible and when performed, calibration of current GIST models appears to be suboptimal. We aimed to develop a prognostic model to predict the recurrence of GIST after surgery with both good discrimination and calibration by uncovering and harnessing the non-linear relationships among variables that predict recurrence.

Methods

In this observational cohort study, the data of 395 adult patients who underwent complete resection (R0 or R1) of a localised, primary GIST in the pre-imatinib era at Memorial Sloan Kettering Cancer Center (NY, USA) (recruited 1982-2001) and a European consortium (Spanish Group for Research in Sarcomas, 80 sites) (recruited 1987-2011) were used to train an interpretable Artificial Intelligence (AI)-based model called Optimal Classification Trees (OCT). The OCT predicted the probability of recurrence after surgery by capturing non-linear relationships among predictors of recurrence. The data of an additional 596 patients from another European consortium (Polish Clinical GIST Registry, 7 sites) (recruited 1981-2013) who were also treated in the pre-imatinib era were used to externally validate the OCT predictions with regard to discrimination (Harrell's C-index and Brier score) and calibration (calibration curve, Brier score, and Hosmer-Lemeshow test). The calibration of the Memorial Sloan Kettering (MSK) GIST nomogram was used as a comparative gold standard. We also evaluated the clinical utility of the OCT and the MSK nomogram by performing a Decision Curve Analysis (DCA).

Findings

The internal cohort included 395 patients (median [IQR] age, 63 [54-71] years; 214 men [54.2%]) and the external cohort included 556 patients (median [IQR] age, 60 [52-68] years; 308 men [55.4%]). The Harrell's C-index of the OCT in the external validation cohort was greater than that of the MSK nomogram (0.805 (95% CI: 0.803-0.808) vs 0.788 (95% CI: 0.786-0.791), respectively). In the external validation cohort, the slope and intercept of the calibration curve of the main OCT were 1.041 and 0.038, respectively. In comparison, the slope and intercept of the calibration curve for the MSK nomogram was 0.681 and 0.032, respectively. The MSK nomogram overestimated the recurrence risk throughout the entire calibration curve. Of note, the Brier score was lower for the OCT compared to the MSK nomogram (0.147 vs 0.564, respectively), and the Hosmer-Lemeshow test was insignificant (P = 0.087) for the OCT model but significant (P < 0.001) for the MSK nomogram. Both results confirmed the superior discrimination and calibration of the OCT over the MSK nomogram. A decision curve analysis showed that the AI-based OCT model allowed for superior decision making compared to the MSK nomogram for both patients with 25-50% recurrence risk as well as those with >50% risk of recurrence.

Interpretation

We present the first prognostic models of recurrence risk in GIST that demonstrate excellent discrimination, calibration, and clinical utility on external validation. Additional studies for further validation are warranted. With further validation, these tools could potentially improve patient counseling and selection for adjuvant therapy.

Funding

The NCI SPORE in Soft Tissue Sarcoma and NCI Cancer Center Support Grants.

Stereotactic body radiation therapy for sarcoma pulmonary metastases

BACKGROUND/PURPOSE

Stereotactic body radiation therapy (SBRT) is standard for patients with inoperable early-stage NSCLC. We hypothesized that SBRT for sarcoma pulmonary metastases would achieve high rates of local control with acceptable toxicity and that patients with oligometastatic disease may achieve prolonged survival following SBRT.

MATERIALS/METHODS

This retrospective review included consecutive patients at our institution treated with SBRT for sarcoma pulmonary metastases. Cumulative incidence of local failure (LF) was estimated using a competing risks framework.

RESULTS

We identified 66 patients treated to 95 pulmonary metastases with SBRT. The median follow-up from the time of SBRT was 36 months (95% CI 34 - 53 months). The cumulative incidence of LF at 12 and 24 months was 3.1% (95% CI 0.9 - 10.6%) and 7.4% (95% CI 4.0% - 13.9%), respectively. The 12- and 24-month overall survival was 74% (95% CI 64 - 86%) and 49% (38 - 63%), respectively. Oligometastatic disease, intrathoracic only disease, and performance status were associated with improved survival on univariable analysis. Three patients had grade 2 pneumonitis, and one patient had grade 2 esophagitis. No patients had ≥ grade 3+ toxicities.

CONCLUSION

To the best of our knowledge, this is the largest series of patients treated with SBRT for pulmonary sarcoma metastases. We observed that SBRT offers an effective alternative to surgical resection with excellent local control and low proportions of toxicity.

Results of an Open-label, Phase Ia/b Study of Pembrolizumab plus Olaratumab in Patients with Unresectable, Locally Advanced, or Metastatic Soft-Tissue Sarcoma

PURPOSE

The study evaluated safety and efficacy of olaratumab + pembrolizumab in patients with unresectable locally advanced/metastatic soft-tissue sarcoma (STS) with disease progression on standard treatment.

PATIENTS AND METHODS

This was open-label, multicenter, nonrandomized, phase Ia/Ib dose-escalation study followed by cohort expansion (olaratumab + pembrolizumab intravenous infusion). Primary objectives were safety and tolerability.

RESULTS

The majority of patients enrolled (n = 41) were female [phase Ia: 9 of 13, phase Ib/dose-expansion cohort (DEC), 17 of 28], aged < 65 years. In phases Ia and Ib, 13 and 26 patients received prior systemic therapy, respectively. Patients received olaratumab 15 mg/kg (phase Ia; cohort 1) or 20 mg/kg (phase Ia; cohort 2 and phase Ib) and pembrolizumab 200 mg (phase Ia/Ib). The median (Q1-Q3) duration of therapy (olaratumab) was 6.0 (3.0-11.9; cohort 1), 14.4 (12.4-20.9; cohort 2), and 14.0 (6.0-21.8) weeks (DEC). No dose-limiting toxicities and few grade ≥ 3 treatment-emergent adverse events [TEAE; 15 mg/kg: 2 (increased lipase); 20 mg/kg: 1 (increased lipase), 1 (colitis), 2 (diarrhea), 3 (anemia)] were reported. Two TEAEs (increased lipase) were related to study discontinuations. Twenty-one patients reported mild (grade ≤ 2) TEAEs [phase Ia, disease control rate (DCR):14.3% (1/7, cohort 1); 66.7% (4/6, cohort 2); no responses were reported; phase Ib, DCR: 53.6% (15/28); objective response rate: 21.4% (6/28; RECIST and irRECIST criteria)]. No response was observed in patients with programmed death ligand-1-positive tumors.

CONCLUSIONS

Antitumor activity was observed in some patients in DEC, and combination was well tolerated with manageable safety profile. Further studies are warranted to evaluate the efficacy and mechanistic impact of platelet-derived growth factor receptor inhibitors with immune checkpoint modulator coadministration.

ATRX guards against aberrant differentiation in mesenchymal progenitor cells

Alterations in the tumor suppressor ATRX are recurrently observed in several cancer types including sarcomas, which are mesenchymal neoplasms. ATRX has multiple epigenetic functions including heterochromatin formation and maintenance and regulation of transcription through modulation of chromatin accessibility. Here, we show in murine mesenchymal progenitor cells (MPCs) that Atrx deficiency aberrantly activated mesenchymal differentiation programs. This includes adipogenic pathways where ATRX loss induced expression of adipogenic transcription factors (Pparγ and Cebpα) and enhanced adipogenic differentiation in response to differentiation stimuli. These changes are linked to loss of heterochromatin near mesenchymal lineage genes together with increased chromatin accessibility and gains of active chromatin marks at putative enhancer elements and promoters. Finally, we observed depletion of H3K9me3 at transposable elements, which are derepressed including near mesenchymal genes where they could serve as regulatory elements. Our results demonstrate that ATRX functions to buffer against differentiation in mesenchymal progenitor cells, which has implications for understanding ATRX loss of function in sarcomas.

Undifferentiated and Dedifferentiated Metastatic Melanomas Masquerading as Soft Tissue Sarcomas: Mutational Signature Analysis and Immunotherapy Response

The distinction between undifferentiated melanoma (UM) or dedifferentiated melanoma (DM) from undifferentiated or unclassifiable sarcoma can be difficult and requires the careful correlation of clinical, pathologic, and genomic findings. In this study, we examined the utility of mutational signatures to identify patients with UM/DM with particular attention as to whether this distinction matters for treatment because the survival of patients with metastatic melanoma has dramatically improved with immunologic therapy, whereas durable responses are less frequent in sarcomas. We identified 19 cases of UM/DM that were initially reported as unclassified or undifferentiated malignant neoplasm or sarcoma and submitted for targeted next-generation sequencing analysis. These cases were confirmed as UM/DM by harboring melanoma driver mutations, UV signature, and high tumor mutation burden. One case of DM showed melanoma in situ. Meanwhile, 18 cases represented metastatic UM/DM. Eleven patients had a prior history of melanoma. Thirteen of 19 (68%) of the tumors were immunohistochemically completely negative for 4 melanocytic markers (S100, SOX10, HMB45, and MELAN-A). All cases harbored a dominant UV signature. Frequent driver mutations involved BRAF (26%), NRAS (32%), and NF1 (42%). In contrast, the control cohort of undifferentiated pleomorphic sarcomas (UPS) of deep soft tissue exhibited a dominant aging signature in 46.6% (7/15) without evidence of UV signature. The median tumor mutation burden for DM/UM vs UPS was 31.5 vs 7.0 mutations/Mb (P < .001). A favorable response to immune checkpoint inhibitor therapy was observed in 66.6% (12/18) of patients with UM/DM. Eight patients exhibited a complete response and were alive with no evidence of disease at the last follow-up (median 45.5 months). Our findings support the usefulness of the UV signature in discriminating DM/UM vs UPS. Furthermore, we present evidence suggesting that patients with DM/UM and UV signatures can benefit from immune checkpoint inhibitor therapy.

Distinct genomic landscapes in radiation-associated angiosarcoma compared with other radiation-associated sarcoma histologies

MYC amplifications have been frequently detected in radiation (RT)-associated angiosarcomas (ASs) by low-resolution molecular methods. However, large-scale next-generation sequencing (NGS) studies to investigate the genomic landscape of RT-AS are scarce, particularly compared with other RT-associated sarcomas. We performed a detailed comparative genomic investigation of RT-AS versus other RT-associated histotypes, as well as sporadic sarcomas with similar histologies. Our institutional targeted DNA-NGS assay database was searched for RT-associated sarcomas. Clinical outcome data, pathologic diagnosis, and the types and frequencies of genomic alterations, including single nucleotide variants (SNVs) and copy number alterations (CNAs), were analyzed. The cohort consisted of 82 patients, 68 (83%) females and 14 (17%) males, aged 37-88 (mean 64) years. Forty-four RT-ASs (38 from breast) and 38 RT sarcomas of other histologies, including 12 malignant peripheral nerve sheath tumors (RT-MPNSTs), 14 undifferentiated pleomorphic sarcomas (RT-UPSs), and 12 osteosarcomas (RT-OSs), were included. Median time intervals from radiation to initial diagnosis in RT-AS (8.0 years) were significantly lower than those in RT-MPNST and RT-UPS (12.5 and 18.5 years), respectively. Each RT-sarcoma histotype harbored distinct mutations and CNAs. RT-associated AS had more frequent MYC, FLT4, CRKL, HRAS, and KMT2D alterations than sporadic AS (enriched in TP53, KDR, ATM, ATRX), whereas the mutational landscapes of MPNST, UPS, and OS were similar in both RT and non-RT settings. CDKN2A/B deletions and TP53 alterations were infrequent in RT-AS compared with other RT sarcomas. Among RT sarcomas, RT-AS harbored the lowest fraction of genome altered (FGA), while RT-MPNST showed the highest FGA. RT-AS had the lowest insertion:SNV and deletion:SNV ratios, while RT-UPS had the highest. The predominant mutational signatures were associated with errors in DNA repair and replication. In conclusion, RT-AS has a distinct genomic landscape compared with other RT sarcomas and sporadic AS. Potential molecular targets for precision medicine may be histotype-dependent. © 2023 The Pathological Society of Great Britain and Ireland.

Circulating tumor DNA analysis of the phase III VOYAGER trial: KIT mutational landscape and outcomes in patients with advanced gastrointestinal stromal tumor treated with avapritinib or regorafenib

BACKGROUND

The current treatment paradigm of imatinib-resistant metastatic gastrointestinal stromal tumor (GIST) does not incorporate KIT/PDGFRA genotypes in therapeutic drug sequencing, except for PDGFRA exon 18-mutant GIST that is indicated for avapritinib treatment. Here, circulating tumor DNA (ctDNA) sequencing was used to analyze plasma samples prospectively collected in the phase III VOYAGER trial to understand how the KIT/PDGFRA mutational landscape contributes to tyrosine kinase inhibitor (TKI) resistance and to determine its clinical validity and utility.

PATIENTS AND METHODS

VOYAGER (N = 476) compared avapritinib with regorafenib in patients with KIT/PDGFRA-mutant GIST previously treated with imatinib and one or two additional TKIs (NCT03465722). KIT/PDGFRA ctDNA mutation profiling of plasma samples at baseline and end of treatment was assessed with 74-gene Guardant360® CDx. Molecular subgroups were determined and correlated with outcomes.

RESULTS

A total of 386/476 patients with KIT/PDGFRA-mutant tumors underwent baseline (pre-trial treatment) ctDNA analysis; 196 received avapritinib and 190 received regorafenib. KIT and PDGFRA mutations were detected in 75.1% and 5.4%, respectively. KIT resistance mutations were found in the activation loop (A-loop; 80.4%) and ATP-binding pocket (ATP-BP; 40.8%); 23.4% had both. An average of 2.6 KIT mutations were detected per patient; 17.2% showed 4-14 different KIT resistance mutations. Of all pathogenic KIT variants, 28.0% were novel, including alterations in exons/codons previously unreported. PDGFRA mutations showed similar patterns. ctDNA-detected KIT ATP-BP mutations negatively prognosticated avapritinib activity, with a median progression-free survival (mPFS) of 1.9 versus 5.6 months for regorafenib. mPFS for regorafenib did not vary regardless of the presence or absence of ATP-BP/A-loop mutants and was greater than mPFS with avapritinib in this population. Secondary KIT ATP-BP pocket mutation variants, particularly V654A, were enriched upon disease progression with avapritinib.

CONCLUSIONS

ctDNA sequencing efficiently detects KIT/PDGFRA mutations and prognosticates outcomes in patients with TKI-resistant GIST treated with avapritinib. ctDNA analysis can be used to monitor disease progression and provide more personalized treatment.

Assessing the Needs of Those Who Serve the Underserved: A Qualitative Study among US Oncology Clinicians

BACKGROUND

The American Society of Clinical Oncology established the 'Supporting Providers Serving the Underserved' (SUS) Task Force with a goal to develop recommendations to support cancer clinicians who deliver care for populations at risk for cancer disparities. As a first step, the Task Force explored barriers and facilitators to equitable cancer care delivery.

METHODS

Clinicians across the United States who deliver care predominantly for low-income and racially and ethnically minoritized populations were identified based on lists generated by the Task Force and the Health Equity Committee. Through purposive sampling based on geographical location, clinicians were invited to participate in 30-60 min semi-structured interviews to explore experiences, barriers, and facilitators in their delivery of cancer care. Interviews were recorded, transcribed, imported into qualitative data management software, and analyzed using thematic analysis.

RESULTS

Thematic analysis revealed three major themes regarding barriers (lack of executive leadership recognition of resources; patient-related socio-economic needs; clinician burnout) and two major themes regarding facilitators (provider commitment, experiential training).

CONCLUSIONS

Findings reveal modifiable barriers and potential solutions to facilitate equitable cancer care delivery for populations at risk for cancer disparities.

A Phase II Study of Epacadostat and Pembrolizumab in Patients with Advanced Sarcoma

PURPOSE

Epacadostat, an indole 2,3 dioxygenase 1 (IDO1) inhibitor, proposed to shift the tumor microenvironment toward an immune-stimulated state, showed early promise in melanoma but has not been studied in sarcoma. This study combined epacadostat with pembrolizumab, which has modest activity in select sarcoma subtypes.

PATIENTS AND METHODS

This phase II study enrolled patients with advanced sarcoma into five cohorts including (i) undifferentiated pleomorphic sarcoma (UPS)/myxofibrosarcoma, (ii) liposarcoma (LPS), (iii) leiomyosarcoma (LMS), (iv) vascular sarcoma, including angiosarcoma and epithelioid hemangioendothelioma (EHE), and (v) other subtypes. Patients received epacadostat 100 mg twice daily plus pembrolizumab at 200 mg/dose every 3 weeks. The primary endpoint was best objective response rate (ORR), defined as complete response (CR) and partial response (PR), at 24 weeks by RECIST v.1.1.

RESULTS

Thirty patients were enrolled [60% male; median age 54 years (range, 24-78)]. The best ORR at 24 weeks was 3.3% [PR, n = 1 (leiomyosarcoma); two-sided 95% CI, 0.1%-17.2%]. The median PFS was 7.6 weeks (two-sided 95% CI, 6.9-26.7). Treatment was well tolerated. Grade 3 treatment-related adverse events occurred in 23% (n = 7) of patients. In paired pre- and post-treatment tumor samples, no association was found between treatment and PD-L1 or IDO1 tumor expression or IDO-pathway-related gene expression by RNA sequencing. No significant changes in serum tryptophan or kynurenine levels were observed after baseline.

CONCLUSIONS

Combination epacadostat and pembrolizumab was well tolerated and showed limited antitumor activity in sarcoma. Correlative analyses suggested that inadequate IDO1 inhibition was achieved.

Bolus versus Continuous Intravenous Delivery of Doxorubicin in Soft-Tissue Sarcomas: Post Hoc Analysis of a Prospective Randomized Trial (SARC021/TH CR-406)

PURPOSE

Continuous intravenous infusion (CIV) of doxorubicin (DOX) versus bolus (BOL) may minimize dose-dependent DOX cardiomyopathy, but it is unclear whether this advantage is evident as employed in typical soft-tissue sarcoma (STS) treatment. The impact of administration mode on adverse events (AE) and efficacy were compared using data from a randomized trial of DOX-based therapy (SARC021/TH CR-406).

EXPERIMENTAL DESIGN

In this post hoc analysis, CIV versus BOL was at discretion of the treating physician. Likelihood of AEs, and objective responses were assessed by adjusted logistic regression. Progression-free (PFS) and overall survival (OS) were compared using Kaplan-Meier, log-rank test, and adjusted Cox regression.

RESULTS

DOX was administered by BOL to 556 and by CIV to 84 patients. Proportions experiencing hematologic, non-hematologic, or cardiac AEs did not differ by administration mode. Hematologic AEs were associated with age, performance status, and cumulative DOX. Non-hematologic AEs were associated with age, performance status, and cumulative evofosfamide. Cardiac AEs were only associated with cumulative DOX; there was no interaction between DOX dose and delivery mode. PFS and OS were similar (median PFS 6.14 months BOL vs. 6.11 months CIV, P = 0.47; median OS 18.4 months BOL vs. 21.4 months CIV, P = 0.62). PFS, OS, and objective responses were not associated with delivery mode.

CONCLUSIONS

CIV was not associated with superior outcomes over BOL within DOX dosing limits of SARC021. Cardiac AEs were associated with increasing cumulative DOX dose. While not randomized with respect to DOX delivery mode, the results indicate that continued investigation of AE mitigation strategies is warranted.

Histopathologic Grading Is of Prognostic Significance in Primary Angiosarcoma of Breast: Proposal of a Simplified 2-tier Grading System

Despite a wide spectrum of clinical presentations, including primary or secondary, most angiosarcomas are considered high grade. One exception is primary breast angiosarcoma, where historically, histologic grading has shown to predict outcome using the Rosen 3-tier system. However, more recent studies have challenged this concept suggesting that even in this specific clinical context angiosarcomas should be considered high grade. This study aimed to critically reevaluate the impact of histologic grade in a clinically uniform cohort managed at a single institution using a newly proposed grading system. Our study included 49 primary breast angiosarcomas diagnosed during 1994 to 2022 (median follow-up: 33 mo), classified as low grade (29%), intermediate grade (20%), and high grade (51%), based on mitotic count, extent of solid components, and necrosis. At last follow-up, 22% patients developed locoregional recurrences, 63% distant metastases, and 47% patients died of disease. As patients with low and intermediate-grade angiosarcomas had relatively similar outcomes, our cohort was further analyzed using a 2-tier system (low grade and high grade). Targeted-DNA next-generation sequencing (505 cancer gene panel) performed in 11 cases found KDR mutations in 78% and PIK3CA mutations in 44% of high-grade lesions. Histologic grade, by either 3-tier or 2-tier grading systems, had a strong impact on survival, with the 2-tier system being an independent predictor of disease-specific survival and overall survival. Based on 2-tier system, the 5-year overall survival was 38% for high-grade angiosarcoma and 74% for low-grade angiosarcoma. PIK3CA mutations alone or concurrent with KDR alterations were identified in angiosarcomas with worse prognosis.

Distinct IDH1/2-associated Methylation Profile and Enrichment of TP53 and TERT Mutations Distinguish Dedifferentiated Chondrosarcoma from Conventional Chondrosarcoma

Dedifferentiated chondrosarcoma (DDCS) is a rare high-grade chondrosarcoma characterized by a well-differentiated chondrosarcoma (WDCS) component that abruptly transitions to a high-grade, noncartilaginous sarcomatous component. To date, the molecular pathogenesis of DDCS and its distinction from conventional chondrosarcoma remain poorly understood. By targeted sequencing, we examined the mutational and copy-number profiles of 18 DDCS, including macrodissected WDCS components, compared with 55 clinically sequenced conventional chondrosarcomas. In conjunction with publicly available external data, we analyzed the methylation and expression profiles of 34 DDCS and 94 conventional chondrosarcomas. Isocitrate dehydrogenase 1/isocitrate dehydrogenase 2 (IDH1/IDH2) mutations were present in 36% conventional chondrosarcomas and 71% DDCS. Compared with conventional chondrosarcomas, DDCS had higher frequencies of TP53 and TERT promoter mutations and CDKN2A/B copy-number losses. Paired analysis of macrodissected WDCS and the high-grade components revealed TERT promoter mutations as early events. Despite phenotypic similarities, the percentage of genome with copy-number alterations in DDCS was significantly lower than that in other high-grade sarcomas. Differential methylation analysis revealed reduction of IDH1/IDH2-associated global hypermethylation characteristically seen in conventional chondrosarcoma and a distinct methylation profile in DDCS. The WDCS and high-grade components in DDCS showed similar methylation profiles. These CpG sites were associated with upregulated expression of genes involved in G2-M checkpoints and E2F targets. Genomic profiling revealed enrichment of TP53, TERT promoter, and CDKN2A/B alterations in DDCS. Integrated methylation and gene expression analysis revealed distinct IDH1/IDH2-associated methylation and transcriptional profiles as early events in DDCS, which may underlie the pathogenesis of dedifferentiation in chondrosarcomas.

Significance

DDCS is a rare, high-grade chondrosarcoma with a dismal prognosis. About 50%-80% of DDCS harbor IDH1/IDH2 mutations. We uncover a significant alteration of IDH-associated methylation profile in DDCS, which we propose is key to the progression to dedifferentiation. In this context, the potential effect of the use of IDH inhibitors is unclear but important to address, as clinical trials of selective IDH1 inhibitors showed worse outcome in DDCS.

TRAF7-mutated Fibromyxoid Spindle Cell Tumors Are Associated With an Aggressive Clinical Course and Harbor an Undifferentiated Sarcoma Methylation Signature: A Molecular and Clinicopathologic Study of 3 Cases

TRAF7 somatic mutations are rare and have been reported in meningiomas, intraneural perineuriomas, and mesotheliomas. Triggered by an index case of an unclassified low-grade mesenchymal tumor with TRAF7 mutation as the only genetic alteration, we searched our files and identified 2 additional cases with similar features. The tumors arose in 2 females and 1 male, aged 63 to 75 years old (median: 67 y). They were infiltrative deep soft tissue masses involving the shoulder, chest wall, and thigh, measuring 7.0 to 9.1 cm in greatest dimensions. One tumor was locally aggressive, and 2 were associated with lung and bone metastases. The tumors displayed alternating fibrous and myxoid stroma with mild to moderate cellularity and consisted of uniform spindle cells with open chromatin, inconspicuous nucleoli and scant cytoplasm. Significant mitotic activity or necrosis were not present. However, the metastatic tumor of 1 case showed an epithelioid morphology and brisk mitotic activity. Immunohistochemically, the tumors showed nonspecific and focal smooth muscle actin or CD34 expression. By DNA sequencing, all 3 cases harbored TRAF7 missense mutations involving the C-terminal WD40 domains as the only somatic mutations, showed nonrecurrent focal copy number alterations, and were negative for gene fusions by targeted RNA sequencing. On methylation profiling, the tumors clustered with the undifferentiated sarcoma and myxofibrosarcoma methylation classes and were distinct from morphologic mimics. On follow-up (5 to 36 mo), 2 patients died of disease following aggressive chemotherapeutic regimens. We describe a novel TRAF7- mutated mesenchymal tumor characterized by aggressive clinical behavior despite the histologic appearance of a low-grade fibromyxoid spindle cell tumor.

Subclonal somatic copy number alterations emerge and dominate in recurrent osteosarcoma

Multiple large-scale tumor genomic profiling efforts have been undertaken in osteosarcoma, however, little is known about the spatial and temporal intratumor heterogeneity and how it may drive treatment resistance. We performed whole-genome sequencing of 37 tumor samples from eight patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and a metastatic or relapse site. We identified subclonal copy number alterations in all but one patient. We observed that in five patients, a subclonal copy number clone from the primary tumor emerged and dominated at subsequent relapses. MYC gain/amplification was enriched in the treatment-resistant clone in 6 out of 7 patients with more than one clone. Amplifications in other potential driver genes, such as CCNE1, RAD21, VEGFA, and IGF1R, were also observed in the resistant copy number clones. Our study sheds light on intratumor heterogeneity and the potential drivers of treatment resistance in osteosarcoma.

Pexidartinib Provides Modest Pain Relief in Patients With Tenosynovial Giant Cell Tumor: Results From ENLIVEN

BACKGROUND

The double-blind, randomized, placebo-controlled phase 3 study of orally administered PLX3397 in patients with pigmented villonodular synovitis or giant cell tumor of the tendon sheath (ENLIVEN) showed that pexidartinib provides a robust objective tumor response in adults with tenosynovial giant cell tumors (TGCT) not amenable to improvement with surgery. Based on these results, in 2019, pexidartinib received accelerated approval in the United States in this population as a breakthrough therapy under an orphan drug designation. However, the ability of pexidartinib to relieve pain in ENLIVEN was not fully detailed, and the relationship between pain relief and objective tumor response was not described.

QUESTIONS/PURPOSES

(1) What level of pain relief was achieved by pexidartinib treatment in ENLIVEN? (2) How was pain relief related to objective tumor responses? (3) How durable was pain relief?

METHODS

The current study included planned primary and exploratory assessments of patient-assessed worst pain at the site of the tumor in the ENLIVEN trial. ENLIVEN was a phase 3 randomized, placebo-controlled clinical trial in which adults with TGCT not amenable to improvement with surgery received pexidartinib or placebo for 24 weeks, after which eligible patients could receive open-label pexidartinib. Of 174 patients assessed for eligibility, 121 were randomized (50% [60] to placebo, 50% [61] to pexidartinib), and 120 were given either placebo or pexidartinib (59 received placebo and 61 received pexidartinib) and were included in an intent-to-treat analysis. Fifty-nine percent (71 of 120) of the overall treated population was female, and 88% (106 of 120) were White. Mean age was 45 ± 13 years. Tumors were mostly in the lower extremities (92% [110 of 120]), most commonly in the knee (61% [73 of 120]) and ankle (18% [21 of 120]). As a secondary outcome, patients scored worst pain at the site of the tumor in the past 24 hours on an 11-point numeric rating scale (NRS). The primary definition of a pain response was a decrease of at least 30% in the weekly mean worst-pain NRS score and increase of less than 30% in narcotic analgesic use between baseline and week 25. Planned exploratory assessments of pain included the frequency of a pain response using alternative thresholds, including a decrease in worst-pain NRS score of 50% or more and a decrease of at least 2 points (minimum clinically important difference [MCID]), the magnitude of pain reduction between baseline and week 25, correlation between worst-pain NRS score and tumor shrinkage by RECIST 1.1 criteria, and the durability of the pain response during the open-label extension. Pain responses during the randomized portion of the trial were compared according to intention-to-treat analysis, with a one-sided threshold of p < 0.025 to reduce the risk of false-positive results. Pain assessment was complete for 59% (35 of 59) of patients in the placebo group and 54% (33 of 61) of patients in the pexidartinib group. Demographic and disease characteristics did not differ between the two treatment groups.

RESULTS

A difference in the primary assessment of a pain response was not detected between pexidartinib and placebo (response percentage 31% [19 of 61] [95% CI 21% to 44%] versus 15% [9 of 59] [95% CI 8% to 27%]; one-sided p = 0.03). In the exploratory analyses, pexidartinib provided a modest improvement in pain (response percentage 26% [16 of 61] [95% CI 17% to 38%] versus 10% [6 of 59] [95% CI 5% to 20%]; one-sided p = 0.02 using the 50% threshold and 31% [19 of 61] [95% CI 21% to 44%] versus 14% [8 of 59] [95% CI 7% to 25%]; one-sided p = 0.02 using the MCID threshold). The least-squares mean change in the weekly mean worst-pain NRS score between baseline and week 25 was larger in patients treated with pexidartinib than placebo (-2.5 [95% CI -3.0 to -1.9] versus -0.3 [95% CI -0.9 to 0.3]; p < 0.001), although the mean difference between the two groups (-2.2 [95% CI -3.0 to -1.4]) was just over the MCID. Improvement in the weekly mean worst-pain NRS score correlated with the reduction in tumor size (r = 0.44; p < 0.001) and tumor volume score (r = 0.61; p < 0.001). For patients in the open-label extension, the change in the worst-pain NRS score from baseline was similar to the change at the end of the randomized portion and just above the MCID (mean -2.7 ± 2.2 after 25 weeks and -3.3 ± 1.7 after 50 weeks of receiving pexidartinib).

CONCLUSION

Based on the current study, a modest reduction in pain, just larger than the MCID, may be an added benefit of pexidartinib in these patients, although the findings are insufficient to justify the routine use of pexidartinib for pain relief.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Role of colony-stimulating factor 1 in the neoplastic process of tenosynovial giant cell tumor

Tenosynovial giant cell tumors (TGCTs) are rare, locally aggressive, mesenchymal neoplasms, most often arising from the synovium of joints, bursae, or tendon sheaths. Surgical resection is the first-line treatment, but recurrence is common, with resulting impairments in patients' mobility and quality of life. Developing and optimizing the role of systemic pharmacologic therapies in TGCT management requires an understanding of the underlying disease mechanisms. The colony-stimulating factor 1 receptor (CSF1R) has emerged as having an important role in the neoplastic processes underlying TGCT. Lesions appear to contain CSF1-expressing neoplastic cells derived from the synovial lining surrounded by non-neoplastic macrophages that express the CSF1R, with lesion growth stimulated by both autocrine effects causing proliferation of the neoplastic cells themselves and by paracrine effects resulting in recruitment of CSF1 R-bearing macrophages. Other signaling pathways with evidence for involvement in TGCT pathogenesis include programmed death ligand-1, matrix metalloproteinases, and the Casitas B-cell lymphoma family of ubiquitin ligases. While growing understanding of the pathways leading to TGCT has resulted in the development of both regulatory approved and investigational therapies, more detail on underlying disease mechanisms still needs to be elucidated in order to improve the choice of individualized therapies and to enhance treatment outcomes.

The genetic landscape of SMARCB1 alterations in SMARCB1-deficient spectrum of mesenchymal neoplasms

SMARCB1 biallelic inactivation resulting in SMARCB1/INI1 deficiency drives a wide range of malignancies, including many mesenchymal tumors. However, the specific types of SMARCB1 alterations and spectrum of cooperating mutations among various types of sarcomas has not been well investigated. We profiled SMARCB1 genetic alterations by targeted DNA sequencing and fluorescence in situ hybridization (FISH) in a large cohort of 118 soft tissue and bone tumors, including SMARCB1-deficient sarcomas (78, 66%): epithelioid sarcomas, epithelioid peripheral nerve sheath tumors, poorly differentiated chordomas, malignant rhabdoid tumors, and soft tissue myoepithelial tumors, as well as non-SMARCB1-deficient sarcomas (40, 34%) with various SMARCB1 genetic alterations (mutations, copy number alterations). SMARCB1 loss by immunohistochemistry was present in 94% SMARCB1 pathogenic cases. By combined sequencing and FISH assays, 80% of SMARCB1-deficient tumors harbored homozygous (biallelic) SMARCB1 loss, while 14% demonstrated heterozygous SMARCB1 loss-of-function (LOF) alterations, and 6% showed no demonstrable SMARCB1 alterations. FISH and sequencing were concordant in the ability to detect SMARCB1 loss in 48% of cases. Epithelioid sarcomas most commonly (75%) harbored homozygous deletions, while a subset showed focal intragenic deletions or LOF mutations (nonsense, frameshift). In contrast, most soft tissue myoepithelial tumors (83%) harbored SMARCB1 nonsense point mutations without copy number losses. Additionally, clinically significant, recurrent co-occurring genetic events were rare regardless of histotype. By sequencing, extended 22q copy number loss in genes flanking the SMARCB1 locus (22q11.23) occurred in one-third of epithelioid sarcomas and the majority of poorly differentiated chordomas. Poorly differentiated chordomas and soft tissue myoepithelial tumors showed significantly worse overall and disease-free survival compared to epithelioid sarcomas. Overall, SMARCB1 LOF alterations predominate and account for SMARCB1 protein loss in most cases: majority being biallelic but a subset were heterozygous. In contrast, SMARCB1 alterations of uncertain significance can be seen in diverse sarcomas types and does not indicate a SMARCB1-deficient entity.

A randomised phase II trial of a trivalent ganglioside vaccine targeting GM2, GD2 and GD3 combined with immunological adjuvant OPT-821 versus OPT-821 alone in metastatic sarcoma patients rendered disease-free by surgery

BACKGROUND

Recurrence after resection of metastatic sarcoma is common. The gangliosides GM2, GD2 and GD3 are strongly expressed across sarcoma subtypes. We hypothesised that generation of anti-ganglioside antibodies would control micrometastases and improve outcomes in sarcoma patients who were disease-free after metastasectomy.

METHODS

We conducted a randomised phase II trial of the immunological adjuvant OPT-821 with a KLH-conjugated ganglioside vaccine targeting GM2, GD2 and GD3, versus OPT-821 alone in patients with metastatic sarcoma following complete metastasectomy. Patients received 10 subcutaneous injections at Weeks 1, 2, 3, 8, 16, 28, 40, 52, 68 and 84 and were followed for evidence of recurrent disease. The primary end-point was relapse-free survival. Secondary end-points included overall survival and serologic response.

RESULTS

A total of 136 patients were randomised, 68 to each arm. The mean age was 51.2, 52.2% were male, 90.4% had relapsed disease, 86.8% had high-grade tumours and 14% had ≥4 metastases resected. Histologies included leiomyosarcoma (33%), spindle cell sarcoma (14%), undifferentiated pleomorphic sarcoma (13%), osteosarcoma (10%), synovial sarcoma (9%), liposarcoma (9%) and others (12%). Most adverse events were Grade ≤2 (83.8% and 70.6% in the vaccine and adjuvant arms, respectively). The most common (≥20% of patients) were injection site reaction (89.7%), fatigue (44.1%) and pyrexia (27.9%) on the vaccine arm, and injection site reaction (69.1%) on the adjuvant only arm. The 1-year relapse-free survival rate (34.5% and 34.8% in the vaccine and OPT-821 monotherapy arm, respectively) did not differ between arms (P = 0.725). One-year overall survival rates were 93.1% and 91.5% in the vaccine and OPT-821 monotherapy arm, respectively (P = 0.578). Serologic responses at week 9 were more frequent on the vaccine arm (96.5% of patients) than in the adjuvant arm (32.8%), and the difference between groups was durable.

CONCLUSIONS

A sustained serologic response to vaccination was induced with the vaccine, but no difference in recurrence-free or overall survival was observed between treatment arms.

CLINICALTRIALS

gov identifier: NCT01141491.

Myxoid pleomorphic liposarcoma is distinguished from other liposarcomas by widespread loss of heterozygosity and significantly worse overall survival: a genomic and clinicopathologic study

Myxoid pleomorphic liposarcoma (MPLPS) is a recently described and extremely rare subtype of liposarcoma with a predilection for the mediastinum. However, the genomic features of MPLPS remain poorly understood. We performed comprehensive genomic profiling of MPLPS in comparison with pleomorphic liposarcoma (PLPS) and myxoid/round cell liposarcoma (MRLPS). Of the 8 patients with MPLPS, 5 were female and 3 were male, with a median age of 32 years old (range 10-68). All except one were located in the mediastinum, with invasion of surrounding anatomic structures, including chest wall, pleura, spine, and large vessels. All cases showed an admixture of morphologies reminiscent of PLPS and MRLPS, including myxoid areas with plexiform vasculature admixed with uni- and/or multivacuolated pleomorphic lipoblasts. Less common features included well-differentiated liposarcoma-like areas, and in one case fascicular spindle cell sarcoma reminiscent of dedifferentiated LPS. Clinically, 4 experienced local recurrence, 4 had distant metastases and 5 died of disease. Compared to PLPS and MRLPS, patients with MPLPS had worse overall and progression-free survival. Recurrent TP53 mutations were present in all 8 MPLPS cases. In contrast, in PLPS, which also showed recurrent TP53 mutations (83%), RB1 and ATRX losses were more common. MRLPS was highly enriched in TERT promoter mutations (88%) and PI3K/AKT pathway mutations. Copy number profiling in MPLPS revealed multiple chromosomal gains with recurrent amplifications of chromosomes 1, 19 and 21. Importantly, allele-specific copy number analysis revealed widespread loss of heterozygosity (80% of the genome on average) in MPLPS, but not in PLPS or MRLPS. Our findings revealed genome-wide loss of heterozygosity co-existing with TP53 mutations as a characteristic genomic signature distinct from other liposarcoma subtypes, which supports the current classification of MPLPS as a stand-alone pathologic entity. These results further expand the clinicopathologic features of MPLPS, including older age, extra-mediastinal sites, and a highly aggressive outcome.

Quality care for patients with tenosynovial giant cell tumor: A multidisciplinary quality improvement initiative

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Background: Tenosynovial giant cell tumor (TGCT) is a rare soft tissue sarcoma that is difficult to treat due to location, high risk of recurrence, and potential for significant morbidity. Recent approvals of novel systemic therapies provide new options for patients who may not be candidates for surgery. However, clinical teams may encounter challenges that inhibit prompt referral, quality of life assessment, and effective multidisciplinary care coordination between surgeons and oncologists. Methods: In September 2020, we surveyed multidisciplinary oncology health teams (n = 25) to assess gaps in TGCT diagnosis, clinical care, and multidisciplinary care coordination. To address identified gaps, teams participated in audit-feedback sessions to develop action plans for improvement. To better understand identified gaps, surveys and education were extended to a nationwide audience of providers caring for patients with TGCT (n = 553). Results: In the health teams survey, top challenges identified included differentiating among appropriate treatment management strategies (46%), coordinating care/transitions of care for patients with TGCT (25%), and making a proper TGCT diagnosis (13%). Confidence gaps echoed these challenges, with less than half of providers indicating high/very high confidence (5-point Likert scale) in their ability to distinguish between nodular and diffuse types of TGCT (47%), align treatment decisions with evidence-based guidelines (47%), and recognize and manage adverse events associated with novel therapies (47%). During audit-feedback sessions, teams developed action plans to improve collaboration between interprofessional teams, improve adverse event management, increase education for supportive care, and facilitate earlier referrals to medical oncologists. When healthcare providers nationwide were surveyed, only 13% reported high or very high confidence in differentiating available treatment options for TGCT. Additionally, the top challenges in coordination care for patients with TGCT included poor follow-up/monitoring for disease recurrence (23%), ineffective communication between multidisciplinary team members (20%), and lack of time for patient-centered measures (19%). Conclusions: These findings reveal important challenges in diagnosis, treatment, and multidisciplinary care of TGCT patients. The methods and findings from this study offer key opportunities for scalable interventions to improve care for patients with TGCT.

Assessing the needs of those who serve the underserved: A national survey among cancer care clinicians

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Background: In 2009, ASCO confirmed that addressing cancer care disparities is critical for the Society and committed to approaches to eliminate such disparities. Yet, gaps remain in identifying the best approaches to do so. It remains unknown which cancer care providers serve patients from “underserved populations'' (defined as individuals who have historically received inadequate health care and health care services), what unmet needs they experience in their cancer care delivery, and how best to engage and support these providers. The objectives of this study were to explore challenges faced by providers serving underserved patients to inform development of a broader online survey and identify solutions that ASCO can implement to better support these providers. Methods: A multi-phase mixed-methods approach was utilized. Phase 1 involved key informant semi-structured interviews with 12 oncology providers caring for adult patients in the US from April to May 2021. Phase 2 involved survey development based on themes identified in Phase 1. The survey assessed: provider needs; processes for eliciting, documenting, and addressing social and economic needs of patients; and how ASCO could best support these providers. Phase 3 involved email distribution of the online survey in May 2022 to 5800 individuals identified through ASCO’s customer database. Eligibility criteria included providing care for adults with cancer in the US and prior consent to receive ASCO survey communications. Results: Of 477 respondents, the majority were ASCO members (88%), in an academic practice (57%), medical oncologists (77%), non-Hispanic (89%) and/or Caucasian/White (67%) and had > 15 years’ clinical experience (57%). A majority (60%) provided ≥25% of their clinical time providing cancer care to underserved populations and routinely engaged with administration to secure resources (61%) and local community organizations to obtain services (42%) for patients. Most (43-77%) indicated that a social worker/case manager was primarily responsible for addressing patient social needs. The majority reported that identification and dissemination of best practices (55%) and development of a return-on-investment business model (60%) would best help address patient needs. Some respondents expressed a desire to collaborate with ASCO on policy reform (32%) and for ASCO to help build or strengthen partnerships with local initiatives (29%). Conclusions: This is the first US-based survey assessing barriers and solutions to delivering cancer care among underserved populations. The findings from this work provide insights about how ASCO can help equip practices to address the social needs of their patients. Further work will be conducted to develop and implement suggested solutions.

Abstract B008: Investigating the evolution of undifferentiated soft tissue sarcomas in a genetically engineered mouse model

Undifferentiated soft tissue sarcomas (USTS) are an aggressive class of sarcomas with few effective treatment options. Because of the rarity of these sarcomas and the paucity of representative disease models, little is known about how they develop. We used single cell transcriptomics to study the initiation and evolution of an USTS in an autochthonous genetically engineered mouse model. We profiled multiple stages of tumor development and identified intermediary cell states that define sarcomagenesis. Interestingly, we identify two discrete evolutionary pathways that arise in parallel in the mouse model. To determine the human relevance of our findings, we are developing machine learning approaches to compare cell states between the mouse model with single-cell transcriptomes that we generated from patient-derived xenografts. This cross-species comparison will uncover core USTS cell states and define their ancestral state transitions. Our ultimate goal is to identify essential molecular features of USTS, which may represent entry points for future therapeutic strategies.

Citation Format: Jason E. Chan, Jonathan Rub, Carleigh Sussman, Olivera Grbovic-huezo, William D. Tap, Cristina Antonescu, Sam Singer, Doron Betel, Tuomas Tammela. Investigating the evolution of undifferentiated soft tissue sarcomas in a genetically engineered mouse model [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B008.

Abstract B022: Subclonal somatic copy number alterations emerge and dominate in relapsed/refractory osteosarcoma

Objective: Multiple large-scale tumor genomic profiling efforts have been undertaken in osteosarcoma, however little is known about the spatial and temporal intratumor heterogeneity and how it may drive treatment resistance. Methods: We performed 30-80x whole genome sequencing (WGS) of 37 tumor samples from 8 patients with relapsed or refractory osteosarcoma. Each patient had at least one sample from a primary site and one sample from a metastatic or relapse site. A set of high confidence single nucleotide variants (SNV), copy number alterations (CNA), structural variations (SV) were called for each sample using our pediatric expanded genomics pipeline and an evolutionary analysis was performed using a custom pipeline of computational tools. Results: Of the 8 patients in our cohort, 4 had localized disease at diagnosis (OSCE4, OSCE5, OSCE6, OSCE9) and 4 had metastatic disease at diagnosis (OSCE1, OSCE2, OSCE3, OSCE10). There were 17 samples from primary sites, 7 were pretreatment biopsies, 10 from on therapy primary resections. 20 samples came from metastatic sites, 15 of which were from lung metastases. Driver gene SNV’s were identified in 5 of 8 patients, including TP53 (OSCE1), ATRX (OSCE3, OSCE10), RB1 (OSCE4), and CDKN2A (OSCE9). There were no new driver SNV’s that emerged post-therapy in any patient. HATCHet, an algorithm that infers clone-specific copy number alterations, identified subclonal CNAs in all but one patient (OSCE2). In the 7 patients with subclonal CNAs, 6 had two copy number clones identified, and 1 patient (OSCE10) had three copy number clones identified. In 5 patients (OSCE1, OSCE4, OSCE5, OSCE6, OSCE10) there is a copy number clone that is subclonal in the primary tumor which emerges and dominates at subsequent relapses. The resistant clone in each of these cases had either MYC gain/amplification. Amplifications in CCNE1 (OSCE1), RAD21 (OSCE4, OSCE5, OSCE10), VEGFA (OSCE1, OSCE9), IGF1R (OSCE6) were also identified as potential drivers in the resistant copy number clones. In two of these patients (OSCE1, OSCE6), this treatment-resistant subclone becomes the dominant copy number clone by the time of primary resection. SNV based phylogenies revealed a heterogenous mix of monoclonal and polyclonal seeding of metastases and monophyletic and polyphyletic modes of dissemination. Over half the new mutations acquired in recurrent disease were attributed to HRD or cisplatin mutational signatures. TP53 structural variants were seen in 6/8 patients (OSCE2, OSCE3, OSCE4, OSCE6, OSCE9, OSCE10). New structural variants involving driver genes were only detected in one relapse sample from patient OSCE10 (DMD deletion). Conclusion: Subclonal copy number clones emerge and dominate in relapsed osteosarcoma, with MYC gain/amplification a defining characteristic in our cohort. Selective pressure from neoadjuvant chemotherapy reveals this clone at the time of primary resection, highlighting that genomic profiling at this time point may be more reflective of its metastatic potential.

Citation Format: Michael D. Kinnaman, Simone Zaccaria, Alvin Makohon-Moore, Gunes Gundem, Juan E. Arango Ossa, Nancy Bouvier, Filemon S. Dela Cruz, Meera Hameed, Julia Lynne Glade Bender, William D. Tap, Paul Meyers, Elli Papaemmanuil, Andrew Kung, Christine A. Iacobuzio-Donahue. Subclonal somatic copy number alterations emerge and dominate in relapsed/refractory osteosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B022.

Abstract B023: Prospective clinical genomic profiling of ewing sarcoma: ERF and FGFR1 mutations as recurrent secondary alterations of potential biological and therapeutic relevance

Background: Ewing Sarcoma (ES) is a primitive sarcoma defined by EWSR1–ETS fusions as the primary driver alteration. To expand our understanding of the genetic and molecular characterization of ES, we conducted a comprehensive analysis of clinical genomic profiling data on tumors from 113 patients using the MSK-IMPACT platform (Integrated Mutation Profiling of Actionable Cancer Targets). Methods: The dataset consisted of ES patients prospectively tested with the FDA-cleared MSK-IMPACT large panel, hybrid capture-based NGS assay. To assess the functional significance of ERF loss, we generated ES cell lines with increased expression of ERF as well as lines with knockdown of ERF. We assessed cell viability, clonogenic growth, and motility and performed transcriptomic and epigenetic analyses. Finally, we validated our findings in vivo using cell line xenografts. Results: Unlike previous ES genomic cohorts, ours included more adult patients (&gt;18 years of age) and more patients with advanced stage at presentation. TP53, STAG2, and CDKN2A were the most common alterations and were associated with worse overall survival at 5-years. Notably, 3% had activating FGFR1 alterations (1 amplification and 2 hotspot activating kinase domain mutations). Mining data generated using a targeted RNAseq assay that includes FGFR1 based on the Archer Anchored Multiplex PCR technology, FGFR1 was highly expressed in the ES cohort (N=42). The 2 patients with activating FGFR1 mutations had relatively high expression of FGFR1. The second novel subset of patients in our cohort were defined by recurrent secondary alterations in ERF, which encodes an ETS domain transcriptional repressor, in 7% of patients (5 truncating mutations, 1 deep deletion, 2 missense mutations). ERF alterations were non-overlapping with STAG2 alterations, suggesting a potentially important biologic role in ES. As the functional significance of FGFR1 mutation in ES has been previously studied, we focused our functional studies on the role of ERF status in ES. In vitro, increased expression of ERF decreased tumor cell growth, colony formation, and motility in two ES cell lines, while ERF loss induced cellular proliferation and clonogenic growth. Transcriptomic analysis of cell lines with ERF loss revealed increased expression of genes and pathways associated with aggressive tumor biology, and epigenetic, chromatin-based studies revealed that ERF competes with EWSR1-FLI1 at ETS binding sites. Conclusion: Our study reveals a previously unexplored role of ERF loss-of-function in ES. Older age in our cohort, and a higher proportion of patients with advanced disease at presentation, could potentially explain the finding of ERF alterations which were associated with aggressive tumor biology in our preclinical studies. Our functional analyses of how ERF modulates EWSR1-FLI1 oncogenicity may open a new window into the pathobiology of ES. Moreover, our data suggest that 3% of ES patients harbor activating FGFR1 mutations, the first targetable kinase alteration in this sarcoma.

Citation Format: Arielle Elkrief, Koichi Ogura, Anita S. Bowman, Richard P. Koche, Ryma Benayed, Audrey Mauguen, Marissa S. Mattar, Inna Khodos, Elisa de Stanchina, Paul A. Meyers, John H. Healey, William D. Tap, Neerav Shukla, Meera Hameed, Ahmet Zehir, Charles Sawyers, Rohit Bose, Emily Slotkin, Marc Ladanyi. Prospective clinical genomic profiling of ewing sarcoma: ERF and FGFR1 mutations as recurrent secondary alterations of potential biological and therapeutic relevance [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B023.

Retrospective observational studies in ultra-rare sarcomas: A consensus paper from the Connective Tissue Oncology Society (CTOS) community of experts on the minimum requirements for the evaluation of activity of systemic treatments

BACKGROUND

In ultra-rare sarcomas (URS) the conduction of prospective, randomized trials is challenging. Data from retrospective observational studies (ROS) may represent the best evidence available. ROS implicit limitations led to poor acceptance by the scientific community and regulatory authorities. In this context, an expert panel from the Connective Tissue Oncology Society (CTOS), agreed on the need to establish a set of minimum requirements for conducting high-quality ROS on the activity of systemic therapies in URS.

METHODS

Representatives from > 25 worldwide sarcoma reference centres met in November 2020 and identified a list of topics summarizing the main issues encountered in ROS on URS. An online survey on these topics was distributed to the panel; results were summarized by descriptive statistics and discussed during a second meeting (November 2021).

RESULTS

Topics identified by the panel included the use of ROS results as external control data, the criteria for contributing centers selection, modalities for ensuring a correct pathological diagnosis and radiologic assessment, consistency of surveillance policies across centers, study end-points, risk of data duplication, results publication. Based on the answers to the survey (55 of 62 invited experts) and discussion the panel agreed on 18 statements summarizing principles of recommended practice.

CONCLUSIONS

These recommendations will be disseminated by CTOS across the sarcoma community and incorporated in future ROS on URS, to maximize their quality and favor their use as control data when results from prospective studies are unavailable. These recommendations could help the optimal conduction of ROS also in other rare tumors.

Comprehensive genomic profiling of EWSR1/FUS::CREB translocation-associated tumors uncovers prognostically significant recurrent genetic alterations and methylation-transcriptional correlates

To elucidate the mechanisms underlying the divergent clinicopathologic spectrum of EWSR1/FUS::CREB translocation-associated tumors, we performed a comprehensive genomic analysis of fusion transcript variants, recurrent genetic alterations (mutations, copy number alterations), gene expression, and methylation profiles across a large cohort of tumor types. The distribution of the EWSR1/FUS fusion partners-ATF1, CREB1, and CREM-and exon involvement was significantly different across different tumor types. Our targeted sequencing showed that secondary genetic events are associated with tumor type rather than fusion type. Of the 39 cases that underwent targeted NGS testing, 18 (46%) had secondary OncoKB mutations or copy number alterations (29 secondary genetic events in total), of which 15 (52%) were recurrent. Secondary recurrent, but mutually exclusive, TERT promoter and CDKN2A mutations were identified only in clear cell sarcoma (CCS) and associated with worse overall survival. CDKN2A/B homozygous deletions were recurrent in angiomatoid fibrous histiocytoma (AFH) and restricted to metastatic cases. mRNA upregulation of MITF, CDH19, PARVB, and PFKP was found in CCS, compared to AFH, and correlated with a hypomethylated profile. In contrast, S100A4 and XAF1 were differentially upregulated and hypomethylated in AFH but not CCS. Unsupervised clustering of methylation profiles revealed that CREB family translocation-associated tumors form neighboring but tight, distinct clusters. A sarcoma methylation classifier was able to accurately match 100% of CCS cases to the correct methylation class; however, it was suboptimal when applied to other histologies. In conclusion, our comprehensive genomic profiling of EWSR1/FUS::CREB translocation-associated tumors uncovered mostly histotype, rather than fusion-type associated correlations in transcript variants, prognostically significant secondary genetic alterations, and gene expression and methylation patterns.

Prospective Clinical Genomic Profiling of Ewing Sarcoma: ERF and FGFR1 Mutations as Recurrent Secondary Alterations of Potential Biologic and Therapeutic Relevance

Ewing sarcoma (ES) is a primitive sarcoma defined by EWSR1-ETS fusions as the primary driver alteration. To better define the landscape of cooperating secondary genetic alterations in ES, we analyzed clinical genomic profiling data of 113 patients with ES, a cohort including more adult patients (> 18 years) and more patients with advanced stage at presentation than previous genomic cohorts.

Pilot study of bempegaldesleukin in combination with nivolumab in patients with metastatic sarcoma

PD-1 blockade (nivolumab) efficacy remains modest for metastatic sarcoma. In this paper, we present an open-label, non-randomized, non-comparative pilot study of bempegaldesleukin, a CD122-preferential interleukin-2 pathway agonist, with nivolumab in refractory sarcoma at Memorial Sloan Kettering/MD Anderson Cancer Centers (NCT03282344). We report on the primary outcome of objective response rate (ORR) and secondary endpoints of toxicity, clinical benefit, progression-free survival, overall survival, and durations of response/treatment. In 84 patients in 9 histotype cohorts, all patients experienced ≥1 adverse event and treatment-related adverse event; 1 death was possibly treatment-related. ORR was highest in angiosarcoma (3/8) and undifferentiated pleomorphic sarcoma (2/10), meeting predefined endpoints. Results of our exploratory investigation of predictive biomarkers show: CD8 + T cell infiltrates and PD-1 expression correlate with improved ORR; upregulation of immune-related pathways correlate with improved efficacy; Hedgehog pathway expression correlate with resistance. Exploration of this combination in selected sarcomas, and of Hedgehog signaling as a predictive biomarker, warrants further study in larger cohorts.

Clinical sequencing of soft tissue and bone sarcomas delineates diverse genomic landscapes and potential therapeutic targets

The genetic, biologic, and clinical heterogeneity of sarcomas poses a challenge for the identification of therapeutic targets, clinical research, and advancing patient care. Because there are > 100 sarcoma subtypes, in-depth genetic studies have focused on one or a few subtypes. Herein, we report a comparative genetic analysis of 2,138 sarcomas representing 45 pathological entities. This cohort is prospectively analyzed using targeted sequencing to characterize subtype-specific somatic alterations in targetable pathways, rates of whole genome doubling, mutational signatures, and subtype-agnostic genomic clusters. The most common alterations are in cell cycle control and TP53, receptor tyrosine kinases/PI3K/RAS, and epigenetic regulators. Subtype-specific associations include TERT amplification in intimal sarcoma and SWI/SNF alterations in uterine adenosarcoma. Tumor mutational burden, while low compared to other cancers, varies between and within subtypes. This resource will improve sarcoma models, motivate studies of subtype-specific alterations, and inform investigations of genetic factors and their correlations with treatment response.

Clinical genomic profiling in the management of patients with soft tissue and bone sarcoma

There are more than 70 distinct sarcomas, and this diversity complicates the development of precision-based therapeutics for these cancers. Prospective comprehensive genomic profiling could overcome this challenge by providing insight into sarcomas' molecular drivers. Through targeted panel sequencing of 7494 sarcomas representing 44 histologies, we identify highly recurrent and type-specific alterations that aid in diagnosis and treatment decisions. Sequencing could lead to refinement or reassignment of 10.5% of diagnoses. Nearly one-third of patients (31.7%) harbor potentially actionable alterations, including a significant proportion (2.6%) with kinase gene rearrangements; 3.9% have a tumor mutational burden ≥10 mut/Mb. We describe low frequencies of microsatellite instability (<0.3%) and a high degree of genome-wide loss of heterozygosity (15%) across sarcomas, which are not readily explained by homologous recombination deficiency (observed in 2.5% of cases). In a clinically annotated subset of 118 patients, we validate actionable genetic events as therapeutic targets. Collectively, our findings reveal the genetic landscape of human sarcomas, which may inform future development of therapeutics and improve clinical outcomes for patients with these rare cancers.

Circulating Tumor DNA Is Associated with Response and Survival in Patients with Advanced Leiomyosarcoma

PURPOSE

We sought to determine whether the detection of circulating tumor DNA (ctDNA) in samples of patients undergoing chemotherapy for advanced leiomyosarcoma (LMS) is associated with objective response or survival.

EXPERIMENTAL DESIGN

Using ultra-low-passage whole-genome sequencing (ULP-WGS) of plasma cell-free DNA from patients treated on a prospective clinical trial, we tested whether detection of ctDNA evaluated prior to the start of therapy and after two cycles of chemotherapy was associated with treatment response and outcome. Associations between detection of ctDNA and pathologic measures of disease burden were evaluated.

RESULTS

We found that ctDNA was detectable by ULP-WGS in 49% patients prior to treatment and in 24.6% patients after two cycles of chemotherapy. Detection of pretreatment ctDNA was significantly associated with a lower overall survival [HR, 1.55; 95% confidence interval (CI), 1.03-2.31; P = 0.03] and a significantly lower likelihood of objective response [odds ratio (OR), 0.21; 95% CI, 0.06-0.59; P = 0.005]. After two cycles of chemotherapy, patients who continued to have detectable levels of ctDNA experienced a significantly worse overall survival (HR, 1.77; 95% CI, 1-3.14; P = 0.05) and were unlikely to experience an objective response (OR, 0.05; 95% CI, 0-0.39; P = 0.001).

CONCLUSIONS

Our results demonstrate that detection of ctDNA is associated with outcome and objective response to chemotherapy in patients with advanced LMS. These results suggest that liquid biopsy assays could be used to inform treatment decisions by recognizing patients who are likely and unlikely to benefit from chemotherapy. See related commentary by Kasper and Wilky, p. 2480.

Circulating tumor DNA (ctDNA) analyses of the phase III VOYAGER trial: KIT mutational landscape and outcomes in patients with advanced gastrointestinal stromal tumor (GIST)

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Background: The genotype of primary mutations predicts imatinib response in untreated metastatic GIST. However, the sequence of salvage treatments in metastatic GIST is based solely on the chronological order of registration trials. ctDNA sequencing offers a powerful diagnostic tool to detect resistance mutations in GIST but has not been shown to correlate with outcomes in clinical trials of pretreated patients (pts). We analyzed ctDNA samples collected at baseline in the phase III VOYAGER trial (NCT03465722) to describe the landscape of KIT alterations and its association with outcomes of pts treated with avapritinib or regorafenib. Methods: In VOYAGER, 476 pts with advanced KIT-mutant GIST were randomly assigned to avapritinib (240 pts) or regorafenib (236 pts) in 3rd-4th line. Baseline plasma was collected and ctDNA analyzed with the Guardant 360 (G360), 74-gene panel. KIT molecular subgroups were determined and correlated with outcomes. PDGFRA-mutant GISTs were excluded from outcomes analysis. Results: Baseline ctDNA analysis was performed in 386/476 pts (81%). ctDNA was detected in 333 pts (86%), with 250 and 18 pts showing at least one KIT (75%) or PDGFRA (5%) variant, respectively. KIT primary mutations were detected in 71% pts (exon 11, 56%; exon 9, 14%; exon 13, 1%) and KIT secondary mutations in 55% of pts. Activation loop (AL, exons 17 and 18) was more commonly affected (44%) than the ATP-binding pocket (ABP, exons 13 and 14; 23%). Among KIT-mutant tumors, multiple KIT mutations were commonly detected within individual tumors (mean, 2.56; range, 1-14). Notably, 17% of pts had > 3 mutations (mean, 6.07; range, 4 to 14). Median PFS and OS were shorter for patients whose ctDNA was positive for V654A or T670I (ABP hot spots) when treated with avapritinib vs. regorafenib: mPFS, 1.9 mo vs. 7.4 mo; log-rank p <.001; mOS, 8.3 mo vs. 11.7 mo; log rank p =.0651. mPFS was shorter for patients with ctDNA positive for KIT exon 17 mutation if concurrently KIT V654A/T670I was absent when treated with avapritinib, with no difference in OS: mPFS, 4.7 mo vs. 6.7 mo; log-rank p =.03; mOS, 19.2 mo vs. NR; log-rank p =.628. mPFS on avapritinib was longer when ABP mutations were absent when compared to those with ABP present (5.6 vs. 1.9 mo; log-rank p <.001). There were no differences considering AL mutations vs. no AL mutations (3.8 vs. 3.9 mo; log-rank p =.622) when treated with avapritinib. Regorafenib showed similar activity regardless of KIT mutational status and the location of KIT mutation. Conclusions: Hybrid capture-based plasma sequencing detects ctDNA in the majority of patients with advanced TKI-resistant GIST, including heterogeneity of KIT mutations. This study is the first to show that ctDNA sequencing correlates with outcomes in pretreated GIST. Identification of ABP (exon13/14) KIT mutations negatively correlates with avapritinib activity.

MOTION: A randomized, phase 3, placebo-controlled, double-blind study of vimseltinib (DCC-3014) for the treatment of tenosynovial giant cell tumor

TPS11590

Background: Tenosynovial giant cell tumor (TGCT) is a rare, locally aggressive neoplasm that occurs in the synovium of joints, bursae, or tendon sheaths. TGCT is caused by upregulation of the colony-stimulating factor 1 (CSF1) gene, resulting in aberrant CSF1 expression and the recruitment of CSF1 receptor (R)-dependent inflammatory cells. Resection is the primary treatment, but nonsurgical treatment options are necessary for patients with symptomatic TGCT not amenable to surgical resection. Vimseltinib is an oral switch control TKI specifically designed to selectively and potently inhibit CSF1R. In a Phase 1/2 study in patients with TGCT, vimseltinib showed encouraging antitumor activity with an overall objective response rate (ORR) of 42% in the cohort receiving 30 mg twice weekly (recommended phase 2 dose; Gelderblom et al, ESMO 2021 Poster). Vimseltinib was also well tolerated, and the majority of the common (≥15%) treatment-emergent adverse events (TEAEs) were Grades 1–2. Among these common TEAEs, the only Grade 3–4 event in the Phase 2, twice-weekly, 30-mg cohort was increased blood creatine phosphokinase (CPK); however, this elevated CPK was not associated with any symptoms (Gelderblom et al, ESMO 2021 Poster). Phase 1/2 efficacy and safety data support further development of vimseltinib; here, we describe the ongoing Phase 3 study for patients with TGCT not amenable to surgical resection. Methods: MOTION (NCT05059262) is a Phase 3, randomized, placebo-controlled, double-blind study that aims to evaluate the efficacy and safety of vimseltinib for the treatment of TGCT not amenable to surgical resection. Participants must be at least 18 years of age and have histologically confirmed and symptomatic TGCT for which surgical resection will potentially cause worsening functional limitation or severe morbidity. Prior CSF1R therapy is not permitted (previous imatinib and nilotinib is allowed). In Part 1 of the study, eligible participants will be randomized 2:1 to receive either vimseltinib 30 mg twice a week or matched placebo for 24 weeks. The primary outcome measure is ORR assessed by central read using Response Evaluation Criteria in Solid Tumors version 1.1 at 25 weeks. Secondary outcome measures include ORR per tumor volume score, range of motion, and patient-reported outcomes. Participants assigned to placebo in Part 1 will have the option to receive vimseltinib in Part 2, a long-term treatment phase in which participants will receive open-label vimseltinib. This international study plans to randomize 120 participants and is currently enrolling. Clinical trial information: NCT05059262.

A phase I/II study of prexasertib in combination with irinotecan in patients with relapsed/refractory desmoplastic small round cell tumor and rhabdomyosarcoma

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Background: Prexasertib (PRX) is an inhibitor of CHK1, prevents DNA repair leading to mitotic catastrophe, and can enhance the activity of DNA-damaging chemotherapy. Translocation driven sarcomas exhibit high levels of replication stress and have demonstrated susceptibility to CHK1 inhibition in preclinical models. Desmoplastic small round cell tumor (DSRCT) and rhabdomyosarcoma (RMS) are aggressive sarcomas of children, adolescents and young adults for which novel therapies are urgently required. Methods: We conducted a phase I/II trial of PRX with irinotecan (irino) in patients ≥ 12 months of age with relapsed or refractory DSRCT or RMS. Eligible patients could have any number of prior therapies, including irino. Dose level 1 was PRX 80 mg/m2 on day 1 + irino 20 mg/m2 for 10 days. Dose levels 2 and 2A were PRX 105 or 150 mg/m2 (>21 years or ≤ 21 years) on day 1 and irino 20 mg/m2 for 10 (level 2) or 5 (level 2A) days. All cycles were 21 days. The primary objectives were to determine the RP2D of PRX with irino, and to determine the best overall response rate (ORR) in 6 months at the RP2D (RECIST v1.1) in DSRCT, with 3 or more responses out of 16 considered promising. Results: 21 patients were enrolled (DSRCT: 19; 2 RMS:2). The RP2D was dose level 2A. Treatment was well tolerated with the most common adverse events being neutropenia (48%), nausea (48%), and fatigue (52%). Cytopenias were managed with the aid of growth factor support in all patients once the RP2D was established. The DSRCT expansion enrolled 13 of 16 planned patients due to discontinuation of PRX supply prior to study completion. Four patients remain on therapy at the time of this submission. Responses in DSRCT patients at all dose levels are shown in Table. Sixteen of 21 enrolled patients, and 5 of 6 patients achieving PR had previously received irino. The median (range) number of cycles was 7 (2-26). Both RMS patients treated at the RP2D experienced SD as best response. The estimated ORR at the RP2D was 23%, and lower boundary of the one-sided 90% confidence interval was 9%, exceeding the unpromising rate of 5%. The two-sided 90% confidence interval was 7 to 49%. In addition, 3 patients had a PR at doses lower than the RP2D, bringing the ORR for all dose levels (n = 19) to 32% (90%CI: 15 to 53%). Conclusions: The RP2D of PRX in combination with irino is PRX 105 or 150 mg/m2 (>21 years or ≤ 21 years) on day 1 and irino 20 mg/m2 for 5 days in 21 day cycles with myelosuppression successfully managed with growth factor support. The study met its primary objective to consider PRX + irino promising in DSRCT and should be further investigated. Clinical trial information: NCT04095221. [Table: see text]

Presence of immune infiltrates, increased expression of transposable elements, and viral response pathways in sarcoma associate with response to checkpoint inhibition

11510

Background: Response to checkpoint inhibition (CPI) in sarcoma is overall low and varies between and within subtypes. Understanding tumor intrinsic determinants of this response may improve efficacy and patient selection. The de-repression of transposable elements (TEs), which are epigenetically silenced repetitive DNA elements of viral origin, is linked to anti-tumor immunity through an antiviral inflammatory response. We hypothesize that baseline expression of TEs and epigenetic regulators correlates with overall response rate (ORR) in sarcoma CPI clinical trials. Methods: This is a retrospective analysis of bulk RNA-sequencing data from pre-treatment biopsies of patients on CPI trials in sarcoma (pembrolizumab plus talimogene laherparepvec, nivolumab plus bempegaldesleukin, and pembrolizumab plus epacadostat). Sixty-seven samples from unique patients representing 12 subtypes were analyzed. The MCP counter deconvolution method and unsupervised clustering were used to group samples by immune phenotypes resulting in immune ‘hot’ and ‘cold’ clusters. ORR was defined by RECIST. To determine if baseline expression of TEs and epigenetic regulators significantly predicted immune types, we implemented a lasso penalized logistic regression. Results: Immune ‘hot’ tumors were characterized by increased immune infiltrates including CD8+ T-cells, B-cells, and NK cells vs ‘cold’ tumors. Patients with ‘hot’ vs ‘cold’ tumors had an ORR of 30.5% (11/36) vs. 3.2% (1/31) (p = 0.003; chi-squared). The best predictors of ‘hot vs ‘cold’ was the increased expression of multiple TE families including MER45A, MER57F, and LTR21B (respective lasso coefficients, 0.27, 0.07, and 0.07). Expression of IKZF1, a chromatin-interacting transcription factor, was also predictive (lasso coefficient, 0.35) and increased expression correlated with improved ORR (p = 0.003; unpaired t-test). TE and IKFZ1 expression was significantly correlated with CD8+ T-cell signaling and antiviral response pathways such as cGAS-STING (MER57F, r2= 0.43, padj = 1.75E-4; IKZF1, r2= 0.63, padj = 6.28E-9) and type II interferon (MER57F, r2= 0.67, padj = 2.51E-10; IKZF1, r2= 0.60, padj = 7.19E-8). Increased expression of cGAS-STING (p = 3.9E-4; unpaired t-test) and type II interferon pathways (p = 1.89E-10; unpaired t-test) was significant in ‘hot’ tumors. Conclusions: Immune ‘hot’ baseline immune profiles of sarcoma are associated with improved ORR to CPI and with increased expression of TEs and IKZF1. These differences in gene expression correlate with increased inflammatory signaling, which suggests a response to TE-encoded viral-like sequences that are typically epigenetically silenced. Induction of TE de-repression and IKZF1 expression through epigenetic targeting warrants pre-clinical investigation as a strategy to promote CPI response in sarcomas.