Lorigerlimab, a bispecific PD-1×CTLA-4 DART molecule in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): A phase 1 expansion (exp) cohort

155

Background: Lorigerlimab (MGD019) is an investigational, bispecific Fc-bearing (IgG4) DART molecule designed to enhance CTLA-4 blockade on dual expressing, tumor infiltrating lymphocytes, while maintaining maximal PD-1 blockade on PD-1 expressing cells. Lorigerlimab has approximate dose proportional PK across 1–10 mg/kg IV dosing Q3W, with sustained PD-1 receptor occupancy evident at doses ≥1 mg/kg Q3W. MGD019-01 is a global first-in-human dose finding and activity estimating study of lorigerlimab in advanced solid tumors (AST). Methods: The exp phase of MGD019-01 evaluates single agent safety, PK, and antitumor effects of lorigerlimab at the recommended dose for exp of 6 mg/kg IV Q3W in 4 tumor specific cohorts. Confirmed responses were noted in each cohort. Preliminary results of the mCRPC cohort are reported here. Response evaluable pts received ≥1 dose and had ≥1 postbaseline imaging evaluation. Measurable lesions were evaluated per RECIST v1.1 and skeletal metastases assessed by bone scan. Prostate specific antigen (PSA) response was defined as a ≥50% (PSA50) or ≥90% (PSA90) PSA decline from baseline with confirmation ≥3 weeks later. Expression of proliferation marker, Ki67, and inducible costimulator (ICOS) by peripheral T cells was assessed by flow cytometry. Results: At data cutoff (9/10/22), 127 pts with AST received ≥1 dose of lorigerlimab 6 mg/kg. Median exposure was 10 weeks (range, 0.1, 94.4) with median of 4 infusions. 6 pts remain on therapy; 36 discontinued for PD (n=13), AEs (n=17), or patient/physician decision (n=6). Treatment related adverse events (TRAE) occurred in 109/127 (85.8%) pts. TRAEs occurring in ≥15% of pts were fatigue, pruritus, hypothyroidism, pyrexia. Rates of grade ≥3 TRAEs and immune-related AEs were 32.3% and 7.9%, respectively. AEs leading to drug discontinuation occurred in 22.8% of pts. There were no fatal AEs related to lorigerlimab. In the mCRPC exp cohort (n=42), pts had a median of 2 prior lines of therapy for CRPC, >80% received prior ART or taxanes; 88% had visceral (liver, 26%; lung, 26%) or nodal disease and 95% had bone metastases. 42 pts were PSA response evaluable; 35 were RECIST evaluable. ORR was 25.7% (9/35; 9 confirmed PRs). Median duration of response was 16.1 weeks (range 6–25+ weeks). 5 responders remain on study, 4 discontinued for unrelated fatal AEs: COVID-19 (2) cardiac arrest (1) C. difficile infection (1). Confirmed PSA50 and PSA90 response rates were 28.6% (12/42) and 21.4% (9/42), respectively. Increased frequencies of Ki67+ and ICOS+ T cells were observed on day 8 posttreatment compared to pretherapy per the flow cytometry analyses from 35 pts. Conclusions: Lorigerlimab demonstrates a manageable safety profile with evidence of encouraging and durable antitumor activity in a chemotherapy refractory mCRPC population. Randomized evaluation of lorigerlimab in mCRPC is warranted. Clinical trial information: NCT03761017 .

A phase 2 study of the MDM2 inhibitor milademetan in patients with TP53-wild type and MDM2-amplified advanced or metastatic solid tumors (MANTRA-2)

TPS3165

Background: Murine double minute 2 (MDM2) is a potent negative regulator of the tumor suppressor p53. MDM2 induces degradation of p53 and promotes tumorigenesis in solid tumors, and preclinical models have shown that inhibition of MDM2 can restore p53 tumor suppressor activity in TP53-wild type (WT), MDM2-amplified tumors. We performed a mutual exclusivity analysis of patients with solid tumors (n = 42,125; AACR Project GENIE) and found that the frequency of co-occurring TP53 mutations decreased with increasing MDM2 copy number. An MDM2 copy number of 12 was chosen as the threshold. An estimated 1.1% of solid tumors meet this molecular criteria, excluding glioblastomas, dedifferentiated liposarcomas, and intimal sarcomas where this signature is enriched. Milademetan (RAIN-32), an oral, selective MDM2 inhibitor, inhibits growth of TP53-WT/ MDM2-amplified cell lines and patient-derived xenograft models from varying tumor types. Furthermore, tumor regression was observed in 3/3 non-liposarcoma patients with MDM2 copy number > 12 in a phase 1 trial of milademetan. MANTRA-2 (RAIN-3202) is a phase 2, multicenter, single-arm, open-label, basket trial designed to evaluate the efficacy or clinical benefit of milademetan in TP53-WT solid tumors with MDM2 amplification (copy number ≥ 12). Methods: Eligible patients must be ≥ 18 years of age with histologically and/or cytologically confirmed locally advanced, incurable or metastatic solid tumors refractory to standard therapy. Local testing demonstrating TP53 WT and MDM2 amplification is required, defined as a MDM2 copy number ≥ 12 or 6-fold increase. Patients with well-differentiated/de-differentiated liposarcomas, intimal sarcomas, or primary central nervous system tumors are excluded. Prior treatment with an MDM2 inhibitor is not permitted. Patients receive milademetan 260 mg orally once daily on Days 1–3 and 15–17 of a 28-day cycle. Tumor response is evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: objective response rate. Secondary endpoints include: duration of response; progression-free survival; growth modulation index; disease control rate; overall survival; safety; health-related quality of life scores. Exploratory endpoints include: biomarkers in blood and/or tumor tissue; pharmacodynamics; pharmacokinetics. Enrollment of 65 patients is planned to ensure that 57 patients have centrally confirmed TP53 WT and MDM2 copy number ≥ 12. The trial opened in November 2021 and is actively enrolling patients. Clinical trial information: NCT05012397.

A phase 1b lead-in to a randomized phase 2 trial of lurbinectedin plus doxorubicin in leiomyosarcoma (LMS)

TPS11592

Background: Single agent or combination chemotherapy regimens, typically including doxorubicin or gemcitabine, represent standard of care options for first- and second-line therapy in patients (pts) with metastatic LMS. However, response rates (ORR) and progression-free (PFS)/overall survival (OS) remain poor. Lurbinectedin (PharmaMar S.A. and Jazz Pharmaceuticals) uniquely binds DNA, inducing DNA double strand breaks leading to apoptosis and delaying progression through phase S/G2 of the cell cycle. Lurbinectedin is a novel structural analog of trabectedin with improved toxicity profile, potency, and pharmacokinetics. In a prior pilot study, we showed that the combination of lurbinectedin and doxorubicin (L+D) was safe, with early signs of clinical activity, particularly in LMS. Thus, we designed this investigator-initiated/investigator-sponsored phase 1b lead-in to optimize doses of L+D, to be followed by a randomized (1:1) phase 2 study of L+D versus doxorubicin monotherapy in anthracycline-naïve LMS. Methods: Pts age > 18 years with locally advanced or metastatic, unresectable LMS (non-GIST soft-tissue sarcoma histologies allowed in Phase 1b), without prior anthracycline or lurbinectedin/trabectedin, ECOG PS < 3, measurable disease by RECIST 1.1, and normal organ function, are eligible. Phase 1b dosing will include a fixed dose of lurbinectedin and two dose levels of doxorubicin. The Phase 1b lead-in follows a standard 3+3 design where dose escalation will occur if 0/3 or 1/6 patients experience a dose-limiting toxicity (DLT). Tumor assessments are conducted every two cycles. Once the recommended phase 2 dose (RP2D) is confirmed, Phase 2 will be initiated. Fifty pts will be randomized 1:1 including doxorubicin +/- lurbinectedin. Randomization will be stratified by uterine v. non-uterine origin of LMS. Pts progressing on single agent doxorubicin will be allowed to cross over to lurbinectedin monotherapy. The Phase 2 primary endpoint is PFS. Secondary endpoints include disease control rate, ORR, OS, PFS2 (for doxorubicin monotherapy patients who cross to lurbinectedin monotherapy). Archival tumor, germline DNA, and ctDNA will be collected for correlative studies exploring genomic markers of sensitivity/resistance. We will provide respective point estimate along with 90% confidence interval for each of the arms. Log-rank test will be performed to test the difference in survival (both PFS and OS) between groups. Regression analyses of survival data will be based on the Cox proportional hazards model. The first pt in dose-level 1 of the Phase 1b lead-in was enrolled in February 2022. Clinical trial information: NCT05099666.

Correlative results from NCI protocol 10250: A phase II study of temozolomide and olaparib for the treatment of advanced uterine leiomyosarcoma

11509

Background: uLMS is an aggressive sarcoma subtype of smooth muscle origin. Chemotherapy provides limited benefit for advanced disease. 18-25% of uLMS harbor deleterious alterations in homologous recombination (HR) DNA repair genes. uLMS exhibits high levels of replicative stress. These findings prompted a phase 2 study of O+T in pretreated uLMS where O+T demonstrated activity: ORR 27%, mPFS 6.9 mos (Ingham M. et. al. ASCO 2021: #11506) Methods: NCI protocol #10250 is a single-arm, multicenter, phase 2 trial evaluating O+T in advanced uLMS pts with progression on ≥1 prior line. Pre-treatment (Pre) and on-treatment (On) biopsies were collected from 22 pts. In prespecified analysis, we evaluated for a relationship between clinical outcomes and HR gene alterations by whole exome sequencing (WES), SLFN11/MGMT expression by RNAseq, and RAD51 foci formation (functional assay). HRD scores were calculated from WES using scarHRD. Gene expression was evaluated using a Spearman rank-order correlation analysis to identify genes associated with PFS (p < 0.01) and overexpressed in sensitive (S: PFS > 240d) or resistant (R: PFS < 240d) pts. Gene set enrichment analysis (GSEA) was performed (q = FDR-adjusted p value). Pts with available results: WES/RNAseq (16), Pre HRD score (13), Pre RAD51 foci (12). Results: 31% (5/16) pts had a mutation (Mut) or homozygous deletion (Hd) in the HR panel: ATRX Mut (2), ATR Mut, PALB2 Hd, RAD51B Hd. Pts with PALB2 and RAD51B Hd had longest PFS on study. Recurrent alterations also occurred in TP53 (56%) and RB1 (19%). Median HRD score in Pre samples was 51 (range 36-66) and 10/13 had HRD scores ≥ 42. Pre and On SLFN11 and MGMT RNA expression were not correlated with ORR/PFS. 6/13 Pre samples were HR-deficient by the RAD51 foci assay. Of pts with PFS ≥ 200d, 4/6 were HR-deficient. In Pre samples, 81 genes were overexpressed in S pts and 73 in R pts. In On samples, 146 genes were overexpressed in S pts and 127 in R pts. In On samples, GSEA identified the epithelial-mesenchymal transition enriched in S pts (q = 3.38e-7) and cell cycle pathways (E2F targets, G2M checkpoint) in R pts (q = 7.43e-4). Only 2 genes, CXCL10 and PCDH15, were differentially expressed between paired Pre and On samples (both increased in On). Gene expression signatures for replicative stress showed borderline association with worse PFS. Conclusions: Most uLMS tumors exhibit HR defects as measured by HRD scores. A subset of pts with greater benefit from O+T were identified by WES for HR genes and the RAD51 assay. There was no correlation between SLFN11 and MGMT expression and outcomes. GSEA identified pathways differentially expressed in S and R pts in On samples. O+T induced CXCL10 which has been associated with T-cell trafficking to tumors. A randomized phase 3 trial of O+T versus investigator’s choice is planned. These results provide insight into which pts may benefit most from this novel drug combination. Clinical trial information: NCT03880019.

MANTRA: A randomized, multicenter, phase 3 study of the MDM2 inhibitor milademetan versus trabectedin in patients with de-differentiated liposarcomas

TPS11589

Background: Murine double minute 2 (MDM2) is a negative regulator of tumor suppressor protein p53. MDM2 induces degradation of p53 and promotes tumorigenesis. MDM2 amplification occurs in many cancers but is documented in up to 100% of well-differentiated or dedifferentiated liposarcomas (WD/DDLPS) [Cancer Genome Atlas Research Network. Cell 2017]. Inhibition of the MDM2-p53 interaction is a promising therapeutic approach to restore p53 tumor suppressor activity in WD/DDLPS. Milademetan (RAIN-32) is a small-molecule MDM2 inhibitor that inhibits the MDM2-p53 interaction and restores p53 function at nanomolar concentrations. In a phase 1 study, milademetan showed promising efficacy in 53 patients with WD/DDLPS when administered on an intermittent schedule (260 mg QD on Days 1–3 and 15–17 on a 28-day cycle), with a median progression-free survival (PFS) of 7.4 months [Gounder et al. AACR-NCI-EORTC 2020]. WD/DDLS are relatively resistant to chemotherapy, and systemic treatment options for patients with advanced disease are limited. MANTRA (RAIN-3201) is a randomized, multicenter, open-label, phase 3 registration study designed to evaluate the efficacy and safety of milademetan versus trabectedin in patients with unresectable or metastatic DDLPS with disease progression on ≥ 1 prior systemic therapies. Methods: Eligible patients are ≥ 18 years of age with histologically confirmed unresectable and/or metastatic DDLPS, with or without a WD component, who have received ≥ 1 prior systemic therapies, including ≥ 1 anthracycline-based regimen, with radiographic evidence of progression by RECIST v1.1 within 6 months before study entry. Prior treatment with trabectedin or an MDM2 inhibitor is not permitted. Patients will be randomly assigned (1:1) to receive milademetan (260 mg once daily orally Days 1–3 and 15–17 on a 28-day cycle) or trabectedin (1.5 mg/m2 as a 24-hour intravenous infusion every 3 weeks). Randomization is stratified by Eastern Cooperative Oncology Group performance status (0 or 1) and number of prior treatments for WD/DDLPS (≤ 2 or > 2). Tumor response will be evaluated by RECIST v1.1 at Weeks 8, 16, 24, and 32, and then every 12 weeks. Primary endpoint: PFS by blinded independent central review. Secondary endpoints: overall survival; disease control rate; objective response rate; duration of response; PFS by investigator assessment; safety; health-related quality of life. Exploratory endpoints: molecular markers in peripheral blood and/or tumor tissue; milademetan pharmacokinetics. To demonstrate a 3-month increase in PFS (from 3 to 6 months) corresponding to a hazard ratio of 0.5, approximately 160 patients will be required to observe 105 events with 93.9% power and 2-sided significance level of 5%. Clinical trial information: NCT04979442.

Phase II study of nivolumab and ipilimumab in children and young adults with INI1-negative cancers

TPS10055

Background: Several aggressive pediatric and young adult cancers are characterized by SMARCB1 inactivation resulting in loss of INI1 expression, including rhabdoid tumors, epithelioid sarcoma and undifferentiated chordoma. These malignancies are associated with a poor prognosis and few effective treatment options for relapsed or refractory disease. Prior studies and emerging data suggest INI1-negative cancers may be uniquely susceptible to treatment with immune checkpoint inhibitors: Many INI1-negative pediatric tumors express PD-L1 and are infiltrated by immune cells, and there are reports of patients with advanced INI1-negative cancers with clinical responses to immune checkpoint blockade (Forrest et al. Clinical Cancer Research, 2020). We hypothesize that INI1 loss predicts tumor response to immune checkpoint inhibition (ICI). Methods: This is an ongoing multicenter, phase II, open-label clinical trial to evaluate the activity of nivolumab and ipilimumab in patients aged 6 months to 30 years with relapsed or refractory INI1-negative cancers (NCT04416568). The study enrolls patients in 2 strata: extracranial solid tumors in Stratum 1 and intracranial solid tumors in Stratum 2. Patients treated with prior ICI are excluded. Patients are treated with intravenous (IV) nivolumab 3mg/kg plus ipilimumab 1mg/kg IV every 3 weeks for 4 cycles followed by nivolumab 3mg/kg (max dose 240mg) IV every 2 weeks for up to 1-year. The primary objective is to evaluate the objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors (RECIST) for Stratum 1 and by Response Assessment in Neuro-Oncology (RANO) criteria for Stratum 2. The trial has a 2-stage design targeting a 25% or greater response rate, with each stratum assessed independently. The analysis for Stage 1 in a given Stratum will be performed after 10 patients are enrolled. If a sufficient number of responders are observed, an additional 10 patients will be enrolled at Stage 2. Secondary endpoints include progression-free survival, overall survival, and disease control rate at 12 months. Correlative aims include assessing tissue and blood biomarkers associated with treatment response. Enrollment began 14 Aug 2020 and is ongoing. Clinical trial information: NCT04416568.

Lurbinectedin (LUR) in combination with Irinotecan (IRI) in patients (pts) with advanced endometrial carcinoma

5586

Background: LUR is a new agent that exerts antitumor activity through inhibition of trans-activated transcription and modulation of tumor microenvironment. Preclinical synergism/additivity in combination with IRI has been reported, thus prompting the conduct of this trial. This synergism had been evaluated and recently reported in patients with Small Cell Lung Cancer, with encouraging results (Ponce et al. WCLC, 2020). Methods: Phase I trial to evaluate escalating doses of LUR on Day (D) 1 plus a fixed dose of IRI 75 mg/m2 on D1 and D8 every 3 weeks (q3w) in pts with advanced solid tumors, enrolled following a standard 3+3 dose escalation design. Phase II to expand in selected indications at the Recommended Dose (RD). In this abstract, the cohort of patients with endometrial carcinoma treated at the RD is presented. Results: 21 pts (all female) with endometrial carcinoma were treated at the RD (LUR 2 mg/m2 + IRI 75 mg/m2 + G-CSF); 57% had ECOG PS=1; median age was 64 years (range 34-74); subtype of tumour was split: 67% (14 pts) endometroid, 33% non-endometroid (3 pts serous-papilar, 3 pts clear-cell and 1 pt undifferentiated); median of 2 prior lines (range, 1−7) per pt. Common G1/2 toxicities were nausea, vomiting, fatigue, diarrhea and anorexia; G3/4 hematological toxicities comprised neutropenia (33%), thrombocytopenia (5%) and anemia (38%). Two episodes of febrile neutropenia occurred (9.5%). G3/4 non hematological toxicities consisted of diarrhea (24%), asthenia (19%), nausea (14%) and vomiting (5%), all were transient and manageable. 1 patient (5%) discontinued treatment due to toxicity drug-related (generalized muscular weakness), but no treatment-related deaths were reported. Objective RECIST responses were documented in 4/21 evaluable pts (19%). With 6 pts censored for progression, median PFS was 4.4 months (95% CI 2.1-9.6 months), and PFS at 6 months was 40.4%. The clinical benefit rate (% of pts with Complete Response (CR), Partial Response (PR) or Stable Disease > 4 months) was 43%, and the Disease Control Rate (% of pts with CR, PR or SD) 81%. 3/21 pts (14%) have been more than 12 months on treatment so far. Conclusions: The combination of Lurbinectedin and Irinotecan is active in heavily pretreated patients with endometrial carcinoma. The combination was well-tolerated and consistent with the known safety profile for this combination. Myelosuppression, diarrhea, nausea and asthenia were predictable and manageable. Updated results of this cohort will be presented at the meeting. Clinical trial information: NCT02611024.

Preliminary results of phase 2 trial of preoperative image guided intensity modulated proton radiation therapy (IMPT) with simultaneously integrated boost (SIB) to the high-risk margin for retroperitoneal sarcomas (RPS)

11550

Background: RPS often have local recurrence (LR) after surgery. Preoperative radiation (RT) to 50.4 Gy can reduce LR risk but is not uniformly effective, especially after (+) margin resections. Therefore, we conducted a multi-institutional, prospective Phase II study to assess efficacy and tolerability of preop IMPT with selective dose escalation to 63 GyRBE to the posterior RPS margin (clinical target volume [CTV] 2) at high risk for (+) margins to further reduce the risk of LR. This dose was tolerable in a prior phase I study (DeLaney T et al, 2017, PMID:28740917). Methods: Primary RPS patients (pts) >18 years received preop IMPT, 50.4 GyRBE in 28 fractions (fx) of 1.8 GyRBE to CTV1 (tumor plus adjacent tissue at risk of subclinical disease) with SIB to CTV2 to 63.0 GyRBE in 28 fx of 2.25 GyRBE. Pts with high-grade tumors could get chemotherapy(CTX) prior to IMPT. To avoid treatment delay, 11 fx of IMRT x-rays could be substituted for IMPT. Pts had restaging and surgery 4-8 weeks after IMPT. Primary study endpoint was local tumor control. Secondary endpoints included clinical and pathologic response, surgical margin status, and disease-free and overall survival. Results: We accrued 60 pts from January 2016 to February 2021. Histology: 35 liposarcoma(LPS) (19 dediff and 16 well diff), 22 leiomyosarcoma(LMS), and 3 undifferentiated pleomorphic sarcoma. IMPT was delivered per protocol in all pts. 51 pts have had surgery, 5 are awaiting surgery, and 4 had no surgery due to metastases(DM) on preop imaging. 22 pts had (+) margins. 2 pts had > 75% necrosis. With 23-month median (range 1-52 months) follow-up after start of RT, there were two LRs. A dediff LPS pt had a well diff LPS LR 26 months postop, resected, and is disease-free. A renal vein/IVC LMS pt treated with CTX and IMPT had LR and DM 4 months postop and died from disease. Surgical Clavien-Dindo morbidity scores: 0(21), 1(9), 2(8), 3a (4), 3b(4), 4a(2), 4(b)1, 5(2); the periop deaths were from sepsis(pneumonia) and duodenal ulcer. The grade 3-4 periop morbidity included abscess(3), treated by catheter(2) or operative(1) drainage, prolonged hospital stays (2 pts with IVC LMS), small bowel obstruction (1), and late sigmoid colon anastomotic failure (1). Readmissions for lymphopenia(1), pneumoperitoneum (1), and volume overload (1). One late neuropathy was seen in a Type II diabetic pt with transient postop weakness after femoral nerve dissection who later had significant lower extremity weakness 3.75 years postop. Study was amended to reduce IMPT dose in diabetic pts. Conclusions: Preoperative IMPT with selective dose escalation to 63 GyRBE to the high risk posterior RPS margin is feasible. Early local control results with this approach appear promising. Some peri-operative morbidity was noted but appears to be in the expected range for RPS resections. Clinical trial information: NCT01659203.

NCI protocol 10250: A phase II study of temozolomide and olaparib for the treatment of advanced uterine leiomyosarcoma

11506

Background: Uterine leiomyosarcoma (uLMS) is an aggressive sarcoma subtype with frequent metastatic relapse. After failure of front-line chemotherapy, remaining options provide limited benefit (trabectedin: ORR 11%, mPFS 4.0 mos; pazopanib: ORR 11%, median PFS 2.9 mos; dacarbazine: ORR 9%, mPFS 1.5 mos). Recent molecular studies suggest uLMS harbors characteristic defects in the homologous recombination (HR) DNA repair pathway, including somatic biallelic BRCA2 deletion in 10%, implicating potential sensitivity to PARP-inhibitor based treatment approaches. In preclinical uLMS models in which temozolomide (T, an oral equivalent to dacarbazine) or the PARP inhibitor olaparib (O) showed limited single agent activity, the combination of T + O was highly effective in inhibiting uLMS tumor growth and promoting apoptosis. Methods: NCI protocol #10250 is a single-arm, open-label, multi-center phase II study evaluating T + O in advanced uLMS. Pts had progression on ≥ 1 prior line and ECOG PS ≤ 2. Pts received T 75 mg/m2 PO daily + O 200 mg PO BID days 1-7 in 21-day cycles. Primary endpoint was ORR. A one-stage binomial design was used. If ≥ 5/22 responded, the treatment was considered promising (95% power; α = 0.06). All pts underwent paired tumor biopsies. Correlative assays to evaluate for HR deficiency (whole exome sequencing/RNAseq, RAD51 foci formation) and for intrinsic PARP inhibitor resistance (SLFN11 expression) will be correlated with response. Results: 22 patients were evaluable (median age 55, median prior treatment lines 3). Median follow-up was 10.8 mos. Primary endpoint, ORR within 6 mos of initiating treatment, was 23% (5/22). Overall ORR was 27% (6/22). Median PFS was 6.9 mos (95% CI: 5.4 mos – not estimable (NE)). Median duration of response (DOR) was 12.0 mos (95% CI: 9.5 mos – NE). Hematologic toxicity was common (grade 3/4 neutropenia, 77%; thrombocytopenia 32%) but manageable with dose modification. Correlative assays are ongoing with plans to present at the meeting. An immunohistochemical assay for RAD51 foci has been adapted for uLMS samples and clearly distinguishes BRCA2- deleted and wild-type tumors. Conclusions: NCI 10250 met the prespecified primary efficacy endpoint of ORR in a population of patients with heavily pre-treated uLMS. Responses are durable (median DOR 12 mos). Correlative assays are being completed to evaluate whether uLMS tumors with HR deficiency or with preserved SLFN11 expression are most sensitive to T + O and may underlie durable responses. A randomized study of the combination is planned. Clinical trial information: NCT03880019.

Updated 5-year local control (LC), metastasis-free survival (MFS), and overall survival (OS) data from a phase I study of nilotinib plus radiation (RT) in high-risk chordoma

e23505

Background: Chordomas are malignant tumors arising from remnant notochordal tissue. Despite improved local control with preoperative/postoperative RT, progression-free survival and OS remain poor in patients (pts) with high-risk features. Chordoma has been identified to express and activate platelet-derived growth factor receptor signaling. We conducted a phase 1 trial to identify the maximum tolerated dose (MTD), safety, and feasibility of nilotinib with RT as either preoperative or definitive treatment for patients with high-risk chordoma. Enclosed is an updated report on LC, MFS, and OS. Methods: We recruited 23 pts with nonmetastatic chordoma to the phase I and dose expansion arms of the study. High-risk was defined as the presence of any of the following: local recurrence after surgery, previous intralesional resection, unplanned incomplete resection, unresectable/marginally resectable disease, or declining surgery due to excessive morbidity. Pts were treated with nilotinib and concurrent RT to 50.4 Gy relative biological effectiveness (RBE) followed by surgery and postoperative RT to a cumulative dose up to 70.2 Gy RBE or definitively up to 77.4 Gy RBE without surgery. On completion of RT, pts were eligible to continue nilotinib until disease progression. Results: The dose escalation arm of the study identified nilotinib 200 mg daily as the maximum tolerated dose (MTD). Eighteen evaluable pts were treated with nilotinib plus RT at the MTD. The objective best response rate was 6% (1 of 18 pts). The 4 and 5-year LC rates were 94.3% (95% CI 83.2-100) and 70.7% (95% CI 20.8-100), respectively. The MFS rate was 74.3 at 4 and 5 years (95% CI 51.8-96.7). The 4 and 5-year OS rates were 70.2% (95% CI 44.4-95.9) and 54.6% (95% CI 20.5-88.6). Conclusions: In updated data from a cohort of high-risk chordoma pts nilotinib 200 mg/d with RT +/- surgery, with long-term follow-up, local control and distant metastasis free survival remains favorable. Clinical trial information: NCT01407198 . [Table: see text]

Efficacy, safety, and immune priming effect of tazemetostat in patients with epithelioid sarcoma

11564

Background: Epithelioid sarcoma (ES) is a rare, aggressive soft tissue sarcoma characterized by loss of inhibitor of integrase 1 (INI1), allowing enhancer of zeste homologue 2 (EZH2) to repress cell differentiation and promote tumorigenesis. Tazemetostat (TAZ) is a selective inhibitor of EZH2 approved by the FDA for treatment of patients (pts) aged ≥16 years with metastatic or locally advanced ES ineligible for complete resection. Methods: This open-label, multicenter, multi-cohort phase 2 study (NCT02601950) evaluated safety and efficacy of TAZ in pts with INI1-negative tumors. ES pts were enrolled in Cohorts 5 and 6; pts in Cohort 6 underwent mandatory pre-dose (at screening) and post-dose biopsies (at Day 1 of cycle 2). Herein, we report the interim efficacy and safety data from Cohort 6. Results: As of July 31 2019, 44 pts were enrolled into Cohort 6 and treated with TAZ 800 mg BID. The objective response rate (ORR) was 11.4%; 4 pts (9.1%) had a partial response and 1 pt (2.3%) had a complete response (Table). Another 17 pts (38.6%) had stable disease (SD). 18 pts had progressive disease; 13 of these pts remained on study beyond progression. Progression-free survival (PFS) and overall survival (OS) at 56 weeks were 19.4% and 59.4%, respectively. In a pooled posthoc analysis of 106 ES pts from Cohorts 5 (n = 62), and 6, ORR was 13.2%. Grade 3–4 adverse events (AEs) were reported in 16 pts (36.4%), most commonly anemia (6.8%; n = 3) and tumor pain (6.8%; n = 3). 3 pts (6.8%) experienced grade 3–4 treatment-related AEs. One pt discontinued study drug and there were no treatment-emergent dose reductions or treatment-related deaths. These safety data from Cohort 6 are consistent with previously reported data from Cohort 5. 19 paired biopsies were included for translational endpoint analyses. Preliminary RNA seq and pathway analyses are currently ongoing and updated data, including additional biomarker data will be presented. Conclusions: Consistent with previously reported data from the completed Cohort 5, TAZ demonstrated clinically meaningful, durable, single agent activity in ES pts. Efficacy data from Cohort 6 continue to mature with 8 patients still on treatment. TAZ was well tolerated with a low incidence of treatment related AEs. Clinical trial information: NCT02601950 . [Table: see text]

Lurbinectedin (LUR) in combination with Irinotecan (IRI) in patients (pts) with advanced solid tumors: Updated results from a phase Ib-II trial

3514

Background: LUR is a novel agent that exerts antitumor activity through inhibition of trans-activated transcription and modulation of tumor microenvironment. Preclinical synergism/additivity in combination with IRI has been reported, thus prompting the conduct of this clinical trial. Methods: Phase Ib-II trial to evaluate escalating doses of LUR on Day (D) 1 plus a fixed dose of IRI 75 mg/m2 on D1 and D8 every 3 weeks (q3w) in pts with advanced solid tumors (+/- G-CSF, if dose-limiting toxicities [DLTs] were neutropenia). Starting dose was LUR 1.0 m/m2 + IRI 75 mg/m2. Results: 77 pts have been treated to date at 5 dose levels, 51 of them at the recommended dose (RD). Baseline characteristics of all 77 pts were: 48% females, 68% ECOG PS=1; median age 57 years (range, 19-75 years); median of 2 prior lines (range, 0−4 lines). The maximum tolerated dose (MTD) was LUR 2.4 mg/m2 + IRI 75 mg/m2 with G-CSF, and the RD was LUR 2.0 mg/m2 + IRI 75 mg/m2 with G-CSF. DLTs in Cycle 1 occurred in 2/3 evaluable pts at the MTD and 3/13 evaluable pts at the RD, and comprised omission of IRI D8 infusion due to grade (G) 3/4 neutropenia (n=3 pts) or G2-4 thrombocytopenia (n=2). At the RD (n=51), common G1/2 non-hematological toxicities were nausea, vomiting, fatigue, diarrhea, anorexia and neuropathy. G3 non-hematological toxicities (diarrhea 10%, fatigue 10%) and G3/4 hematological abnormalities (neutropenia 49%, thrombocytopenia 10%) were transient. Conclusions: The combination of LUR and IRI had acceptable tolerance, with no unexpected toxicities. Transient myelosuppression was dose-limiting. The RD is LUR 2.0 mg/m2 on D1 + IRI 75 mg/m2 on D1 and D8 q3w with G-CSF. Antitumor activity was observed at the RD in SCLC pts, as well as in endometrial carcinoma pts. Hints of activity were also observed in STS pts. Updated results will be presented. Clinical trial information: NCT02611024 . [Table: see text]

Phase II study of eribulin and pembrolizumab in patients (pts) with metastatic soft tissue sarcomas (STS): Report of LMS cohort

11559

Background: Responses to single agent PD-1/PD-L1 inhibitors in STS remain limited with occasional responses in undifferentiated pleomorphic sarcomas (UPS), liposarcomas (LPS), and other sarcomas, and rare responses in leiomyosarcoma (LMS). Since cytotoxics and/or targeted therapies such as CDK4/6 inhibitors may alter the tumor microenvironment (TME) and potentiate the effect of immunotherapy, combination approaches may be needed to potentiate STS immunotherapy. The mechanism by which eribulin controls LPS may involve TME modification, and therefore it is attractive to test in combination with pembrolizumab in STS subtypes. This report summarizes the results from the LMS cohort from this ongoing trial. Methods: Pts treated with at least one prior therapy received eribulin 1.4mg/m2 (day 1, 8) and pembrolizumab 200mg (day 1), every 21 days. Pts continued therapy until progressive disease, death, or unacceptable toxicity. Primary endpoint was progression-free survival (PFS) at 12 weeks, with 60% PFS at 12 weeks required to deem the combination promising. Tumor assessments (RECIST 1.1) were performed at screening and every 6 weeks thereafter. Secondary endpoints included overall survival (OS), objective response rate (ORR), and clinical benefit rate (CBR). Results: Nineteen pts with LMS were enrolled from May 2019 to Sept 2019. The median age was 62 (range 48-80). Eleven (58%) patients had uterine LMS. The median # of prior therapies was 4 (range 1-7). The median follow-up was 19.7 weeks. The PFS at 12 weeks was 42.1% (90% CI: 27.0%-65.5%), with median PFS of 11.1 weeks. Median OS was not reached during the follow-up period. There was 1 partial response, and 5 confirmed stable disease for ORR of 5.3% and CBR of 26.3%, after 12 weeks. The rate of grade 3 or higher toxicity was 68% overall, most commonly neutropenia, anemia, weight loss, diarrhea, elevations of lipase, and alkaline phosphatase. These side effects were reversible. The most common adverse events were fatigue, neutropenia, anorexia, AST increase, and nausea. Conclusions: Eribulin and pembrolizumab in LMS did not meet the predefined endpoint for efficacy. The LPS and “other STS subtype” cohorts of this trial are actively enrolling. Clinical trial information: NCT03899805 .

Conditional survival of patients with nonmetastatic bone osteosarcoma

e23511

Background: Conditional survival provides a dynamic prediction of prognosis for patients surviving a defined period of time after diagnosis. This study aimed to determine the conditional survival and prognostic factors over time among patients with non-metastatic bone osteosarcoma. Methods: We reviewed 714 bone osteosarcoma patients treated from 1985 to 2016. Patients with metastatic disease at diagnosis or limited follow up were excluded, resulting in 587 cases for analysis. Clinical and pathological variables were recorded. Predictive variables included age at diagnosis, gender, previous radiation history, tumor site, tumor size, histologic subtype, histologic grade, resection margin, chemotherapy, and radiation therapy. The multivariate Cox proportional hazards regression was used to analyze prognostic factors of conditional overall survival and progression-free survival at baseline and 5 years after diagnosis. Results: The estimated 5-year conditional overall survival increased from 71.0% (95% CI: 67.5%-75.0%) at baseline to 86.9% (95% CI: 82.6%-90.5%) at 5 years, which means if a patient with non-metastatic bone osteosarcoma survived 5 years, the chance of surviving another 5 years was 86.9%. If the patient was progression-free for 5 years, the 5-year conditional overall survival was even higher, 93.2% (95% CI: 89.5%-96.4%), and the 5-year conditional progression-free survival improved from 57.1% (95% CI: 53.3%-61.0%) at baseline to 91.2% (95% CI: 87.5%-94.6%) at 5 years. Prognostic factors for mortality and disease progression change as survival time increases. At baseline, age (p < 0.001 and p = 0.003), histologic subtype (p < 0.001 and p = 0.001), grade (p < 0.001 and p < 0.001), tumor size (p = 0.002 and p = 0.002), resection margin (p < 0.001 and p < 0.001) and chemotherapy (p = 0.001 and p = 0.001) were predictive of both overall survival and progression-free survival. However, only age (p < 0.001) and histologic subtype (p = 0.015) remained significant for mortality and resection margin (p = 0.001) for disease progression at 5 years. Conclusions: The survival probability of osteosarcoma improves as survival time increases. Estimates of conditional survival can provide useful information for individualized surveillance strategies, risk evaluation, patient counseling, and making clinical decisions.

Vorasidenib (VOR; AG-881), an inhibitor of mutant IDH1 and IDH2, in patients (pts) with recurrent/progressive glioma: Updated results from the phase I non-enhancing glioma population

2504

Background: Isocitrate dehydrogenase 1 and 2 mutations (m IDH1/2) occur in approximately 70% and 4% of low-grade gliomas (LGGs), respectively, promoting oncogenesis via increased production of D-2-hydroxyglutarate. In this ongoing phase 1 trial, VOR, a potent, oral, reversible, brain-penetrant, first-in-class dual inhibitor of mIDH1/2, is being evaluated in advanced m IDH1/2 solid tumors, including gliomas. Safety and preliminary results were presented previously (Mellinghoff et al., J Clin Oncol 2018). Here, we report updated data for the non-enhancing glioma pt population. Methods: Pts with recurrent/progressive m IDH1/2 glioma received VOR daily (continuous 28-day cycles). Key eligibility criteria included: ≥18 years; histologically or cytologically confirmed glioma with documented m IDH1/2; ECOG 0-2; and evaluable disease by RANO-LGG criteria. Dose escalation cohorts enrolled using a Bayesian logistic regression model (BLRM) escalation guided by the overdose control (EWOC). Tumor response was evaluated by MRI every 8 weeks using RANO-LGG criteria by local assessment. Results: As of 28 Nov 2019, 22 pts with non-enhancing glioma had received VOR and 8 (36%) remain on treatment. M/F, 8/14; grade 2/3, 17/5; median age, 47 years; m IDH1/2, 20/1; 1p19q intact, 9/22; median (range) number of prior systemic therapies, 2 (1–4). Common (≥5 pts) treatment-emergent adverse events (AEs) of any grade and regardless of causality included increased ALT/AST (63.6%/59.1%), headache (45.5%), nausea (40.9%), neutropenia (31.8%), fatigue and hyperglycemia (27.3% each), and seizures and decreased white blood cell count (22.7% each). Transaminase elevations were grade 1 in severity at dose levels < 100mg and were less frequent (5 [38.5%] of 13 pts). Three subjects had related grade ≥3 AEs; 2 discontinued due to AEs. Objective response rate was 13.6% (1 partial response, 2 minor responses), and 17 (77.3%) pts achieved stable disease. 60.5% of pts were progression free and alive at 24 months. Conclusions: In this previously treated population with non-enhancing glioma, VOR was associated with a favorable safety profile. The study results also show encouraging preliminary activity within that population, with PFS duration extending to 24 months or longer in 60% of participants. A global randomized phase 3 study of VOR in grade 2 non-enhancing glioma pts who have had surgery only is currently enrolling (NCT04164901). Clinical trial information: NCT02481154 .

CBT-1 in combination with doxorubicin in patients with metastatic, unresectable sarcomas who previously progressed on doxorubicin

TPS11077

Background: The response rates of advanced soft tissue sarcomas (STS) to single-agent, first-line anthracycline are typically less than 25%. P-glycoprotein 1 (P-gp), a cell membrane drug efflux pump, is believed to be a resistance mechanism in STS. CBT-1 is a small molecule, orally administered, P-gp antagonist currently under clinical development. This is a multi-institutional open label phase I study of CBT-1 in combination with doxorubicin in patients with anthracycline-refractory sarcoma. The study is designed to determine a maximum tolerable dose (MTD), recommended phase II dose (RP2D), and the safety/tolerability of the combination of CBT-1 and doxorubicin. The study will evaluate anti-cancer activity as a secondary objective as measured by Disease Control Rate (DCR; complete response [CR] + partial response [PR] + stable disease [SD]) at 12 weeks. Objective Response Rate (ORR; CR+PR) and Progression Free Survival (PFS) will be monitored. Correlative studies include assessment of pharmacokinetic and pharmacodynamicendpoints. Methods: Patients 18 years or older with locally advanced metastatic, unresectable STS, prior progression on ≤ 150 mg/m2 of doxorubicin (or another anthracycline equivalent), ECOG PS ≤ 1 and normal organ function, are eligible for this study. Dosing includes fixed doxorubicin (37.5 mg/m2 IV day 5 and day 6) and escalation of oral CBT-1 on days 1-7 of a 21 day cycle. This study follows a standard 3+3 phase I design where dose escalation will occur if < 0/3 or 1/6 patients experience a dose-limiting toxicity (DLT). Tumor assessments are conducted at Week 6 and Week 12. For patients with response or stable disease, treatment is allowed to continue for 4-5 cycles to a maximum of 450 mg/m2 lifetime doxorubicin exposure. Once RP2D is defined, an additional 10 patients will be enrolled into the dose expansion phase. To date, Cohorts 1 (50 mg CBT-1) and 2 (100 mg CBT-1) have been completed with one DLT of grade 4 neutropenia lasting longer than 7 days in Cohort 1. Enrollment to Cohort 3 began December 2018. (References: Oldham, R. K., Reid, W. K., Preisler, H. D., and Barnett, D. (1998) Cancer Biother. Radiopharm. 13, 71-80; Kelly, R. J., Robey, R. W., Chen, C. C., Draper, D., Luchenko, V., Barnett, D., Oldham, R. K., Caluag, Z., Frye, R. A., Steinberg, S. M., Fojo, T., Bates, S. E. (2012) The Oncologist 17 (4) 512-e523; Robey, R. W., Shukla, S., Finely, E. M., Oldham, R. K., Barnett, D., Ambudkar, S. V., Fojo, T., Bates, S. E., (2008) Biochemical Pharmacology 75, 6, 1302-1312). Clinical trial information: NCT03002805.

A phase I, first-in-human, open label, dose-escalation and cohort expansion study of MGD019, a bispecific DART protein binding PD-1 and CTLA-4 in patients with unresectable or metastatic neoplasms

TPS2661

Background: Immune checkpoint molecules, including CTLA-4 and PD-1, attenuate the duration and strength of adaptive immune responses to limit immune-mediated tissue damage. Tumors may inhibit cellular immune activation by expressing ligands that bind checkpoint molecules and inhibit T-cell function in the tumor microenvironment. Blockade of these inhibitory pathways is the primary mechanism of action of several novel cancer immunotherapy agents. Combined blockade of PD-1 and CTLA-4 with two checkpoint inhibitors, ipilimumab and nivolumab, increases antitumor activity beyond either single agent alone in patients with metastatic melanoma or other malignancies. MGD019, a novel bispecific molecule that co-engages and coordinately inhibits both PD-1 and CTLA-4 signaling, was developed to potentially improve antitumor activity and/or safety relative to the monoclonal antibody combination. MGD019 is an Fc-bearing tetravalent DART molecule (bivalent for each antigen) that can independently block either checkpoint molecule, with preferential co-blockade in cells co-expressing both molecules demonstrated in vitro. It is hypothesized that MGD019 might be clinically active in either checkpoint naïve or checkpoint experienced patients after prior PD-1/PD-L1 inhibitors. Methods: This Phase 1 study will characterize safety, dose limiting toxicities, and maximum tolerated dose (MTD)/maximum administered dose (MAD) of MGD019. Dose Escalation will enroll patients with advanced solid tumors of any histology in sequential escalating doses in cohorts of 3 to 9 patients in a 3+3+3 design. Once the MTD/MAD is reached, a Cohort Expansion phase will characterize safety and initial antitumor activity per RECIST v1.1 and irRECIST in patients with specific tumor types anticipated to be sensitive to dual checkpoint blockade. Additional endpoints include pharmacokinetics; immunogenicity; impact of MGD019 on various measures of immune-regulatory effects in peripheral blood and biopsy specimens; and relationship between antitumor activity and gene profiles, tumor mutational burden, and PD-1, PD-L1, and CTLA-4 expression on tumor cells and immune cell infiltrates within biopsy specimens. Patients will be followed for survival approximately every 3 months for 2 years. Clinical trial information: NCT03761017.

Safety and efficacy of tazemetostat, a first-in-class EZH2 inhibitor, in patients (pts) with epithelioid sarcoma (ES) (NCT02601950)

11003

Background: ES is a rare soft tissue sarcoma that metastasizes in approximately 30% to 50% of cases. More than 90% of ES tumors lack expression of INI1, an important component of epigenetic regulation. Loss of INI1 function allows another epigenetic modifier, EZH2, to become an oncogenic driver in tumor cells. Tazemetostat, a first-in-class, selective, oral inhibitor of EZH2, has demonstrated tumor regression and favorable safety in phase 1/2 trials. Methods: Data from a phase 2 open-label, multicenter trial of pts with locally advanced or metastatic ES are reported. Efficacy was assessed with primary and secondary endpoints including objective response rate (ORR) by RECIST 1.1, disease control rate (DCR; objective confirmed response of any duration or stable disease [SD] lasting ≥32 weeks), duration of response (DOR), progression-free survival (PFS), overall survival (OS); safety and tolerability were also evaluated. Results: As of September 17, 2018, 62 INI1-negative ES pts were enrolled and treated with tazemetostat 800 mg BID. The median number of prior lines of therapy was 1 (range: 0-9). There were 9/62 (15%) confirmed partial responses (PRs) with an ORR of 15% and DCR of 26%. The DOR ranged from 7.1+ weeks to 103.0+ weeks (median: not reached) with a median OS of 82.4 weeks (95% CI: 47.4, not estimable) for all 62 pts. Tazemetostat was generally well tolerated. Treatment-emergent adverse events (TEAEs) were generally mild to moderate with the most commonly reported adverse events (AEs; ≥10% incidence) regardless of attribution being fatigue (24/62; 39%), nausea (22/62; 35%), and cancer pain (20/62; 32%). Any treatment-related TEAEs of grade ≥3 were reported in 10/62 (16%) pts. TEAEs grade ≥3 reported in ≥2 pts included anemia (6%) and decreased weight (3%). There were no drug-related deaths and a low discontinuation rate (1.7%). Conclusions: In the largest prospective clinical trial of ES to date, tazemetostat achieved disease control in 26% of pts with advanced ES who entered this study. Durable clinical response of the drug was documented. Tazemetostat demonstrated favorable safety with few pts with treatment-related AEs grade ≥3. Clinical trial information: NCT02601950.

Phase 2 multicenter study of the EZH2 inhibitor tazemetostat in adults with INI1 negative epithelioid sarcoma (NCT02601950)

11058

Background: Epithelioid sarcoma (ES) is a rare soft tissue sarcoma (STS) typically seen in young adults accounting for < 1% of all STS. While local disease may be indolent, ES can rapidly spread and patients (pts) with distant metastasis are often resistant to systemic treatment with 1 year survival of < 50%. The defining molecular feature of ES is the absence of tumor expression of INI1, a SWI/SNF subunit member involved in chromatin remodeling. Tazemetostat, a potent and selective EZH2 inhibitor, has demonstrated tumor regressions in INI1 negative preclinical malignant rhabdoid tumors (MRT) models and phase 1 clinical activity in MRT and ES pts. The proposed mechanism of tazemetostat sensitivity is INI1 loss inducing compromised SWI/SNF activity and tumor dependence on PRC2 activity (of which EZH2 is the catalytic subunit). Preliminary phase 2 safety and efficacy of tazemetostat in ES pts is reported here. Methods: This is a phase 2 multicenter open-label single arm study of tazemetostat (800 mg po BID) in adult pts with ES whose tumors harbor evidence of INI1 loss. Pts enroll into 1 of 5 cohorts of different tumor types with INI1 loss/reduction, up to 30 pts each, using a 2-stage Green-Dahlberg design. For the ES cohort, primary endpoint is disease control rate (DCR) defined as objective response of any duration or stable disease (SD) lasting ≥32 wks. Success at stage 2 required DCR in ≥5/30 treated pts. Key secondary endpoints include safety/tolerability, ORR, PFS, OS, PK and response biomarkers e.g. H3K27me3. Results: In 31 ES pts with a median of 1 prior systemic therapy, stage 2 DCR criteria was surpassed with a RECIST confirmed PR (4 pts) and SD ≥32 wks (2 pts) observed to date. 13 pts are still on treatment therefore DCR and ORR will be updated. Tazemetostat was well tolerated with grade 1/2 fatigue (39%), nausea (26%) and vomiting (19%) as the most frequently reported AEs regardless of attribution. Conclusions: In the largest prospective clinical trial of ES to date, tazemetostat monotherapy shows promising antitumor activity, including confirmed responses and long-term SD, with favorable safety/tolerability in ES. Enrollment has been expanded to 60 ES pts given the clinical activity described here. Clinical trial information: NCT02601950.

Phase 2 multicenter study of the EZH2 inhibitor tazemetostat in adults with synovial sarcoma (NCT02601950)

11057

Background: Synovial sarcoma (SS) accounts for 5-10% of all soft tissue sarcomas (STS). Metastatic and/or locally advanced disease occurs in up to 70% of patients (pts), with reported median overall survival (OS) as short as 22 months. SS18-SSX translocations, a defining molecular feature of SS, generate a fusion protein that competes with native SS18 during SWI/SNF complex assembly disrupting complex function. SWI/SNF complexes containing the fusion protein lack INI1 and cellular INI1 expression levels are reduced to varying degrees in SS. This mechanism of INI1 reduction is distinct to that observed in malignant rhabdoid tumors, epithelioid sarcoma or other INI1 negative tumors. Tazemetostat, a potent and selective EZH2 inhibitor, has demonstrated activity in preclinical SS models with the proposed mechanism of sensitivity being via INI1 reduction inducing compromised SWI/SNF activity and tumor dependence on EZH2. Methods: This is a phase 2 multicenter open-label non-randomized study with 5 cohorts of different tumor types with INI1 loss/reduction or evidence of SS18 rearrangement. Adult pts in the SS cohort were treated with tazemetostat (800 mg po BID). Up to 30 pts were enrolled using a 2-stage Green-Dahlberg design. The primary endpoint is complete response, partial response or stable disease (SD) at 16 wks. Success at the end of stage 2 requires ≥9 of 30 treated pts meet this criterion. Key secondary endpoints include overall response rate, PFS, OS, safety/tolerability, PK and biomarkers of response. Results: In 33 treated SS pts with a median of 2 prior systemic treatments, best response of SD was observed in 11 pts (33%) with 5 pts (15%) having SD lasting ≥16 wks. No objective responses were observed. The protocol-defined success criterion at the end of study was not met. Tazemetostat was well-tolerated with grade 1/2 cough (36%), dyspnea (33%) and fatigue (33%) as the most frequently reported adverse events regardless of attribution. Conclusions: Tazemetostat was well tolerated with a favorable safety profile. Although there were no objective responses in heavily pretreated pts, the observation of SD in a subset of pts suggests further studies with tazemetostat in combination may be warranted in SS. Clinical trial information: NCT02601950.

A phase 1b study of napabucasin plus weekly paclitaxel in patients with advanced thymoma and thymic carcinoma

e20001

Background: Napabucasin is a first-in-class cancer stemness inhibitor, identified by its ability to inhibit STAT3-driven gene transcription and spherogenesis of cancer stem cells (Li et al PNAS 112 (6):1839, 2015). Synergistic anti-tumor activity of napabucasin plus paclitaxel was observed in pre-clinical and early clinical testing. The STAT3 pathway is considered important in thymic carcinoma and thymoma, rare cancers with few treatment options. In 1st line, the objective response rate (ORR, partial response [PR] + complete response [CR] per RECIST) with carboplatin-paclitaxel was 22% in thymic carcinoma and 43% in thymoma (Gemma, 2011). A phase 1b cohort was established to evaluate safety and preliminary signs of activity of napabucasin plus paclitaxel in these patients (pts). Methods: Pts with previously-treated advanced thymoma or thymic carcinoma were enrolled with napabucasin (240 - 480 mg orally twice daily) plus paclitaxel (80 mg/m2 IV weekly for 3 of every 4 weeks). Adverse events were evaluated using CTCAE v4.03 and tumor assessments were obtained every 8 wks per RECIST 1.1. Results: A total of 9 pts (thymic carcinoma = 5, thymoma = 4) with a median 3 prior lines of systemic therapy were enrolled. In thymic carcinoma, the starting napabucasin dose was 480 mg BID (n = 2), and 240 mg BID (n = 3). Treatment was well tolerated and 1 pt required dose-reduction. There were no grade 3 AEs reported. As of data cut-off, 3 pts are off-study with progression and 2 remain on treatment. PRs were observed in 4 of 5 pts (ORR = 80%) and the median time on treatment is > 7.0 mo. In thymoma, 4 pts received napabucasin 240 mg BID. AEs included grade 3 diarrhea and dehydration in 1 pt. As of data cut-off, 1 pt was off-study with progression, 2 died (perforated bowel; autoimmune myocarditis secondary to Issac’s syndrome), and 1 pt remains on treatment. PR was observed in 1 pt (ORR 25%). Conclusions: Napabucasin plus weekly paclitaxel has demonstrated clinical safety and encouraging signs of anti-tumor activity in patients with advanced thymic carcinoma and thymoma. Further clinical evaluation of the combination regimen is warranted in this population. Clinical trial information: NCT01325441.

A phase 1b/2 study of napabucasin with weekly paclitaxel in advanced, previously treated non-squamous non-small cell lung cancer

9052

Background: Napabucasin is a first-in-class cancer stemness inhibitor, identified by its ability to inhibit STAT3-driven gene transcription and spherogenesis of cancer stem cells (Li et al PNAS 112 (6):1839, 2015). Napabucasin has shown potent synergistic preclinical anti-tumor activity with paclitaxel (PTX). In a phase Ib dose escalation study in patients (pts) with advanced solid tumors, napabucasin plus weekly PTX was well tolerated. A phase II expansion cohort was opened for pts with advanced non-small cell lung cancer (NSCLC). Methods: Pts with metastatic non-squamous NSCLC were enrolled to confirm safety and preliminary anti-cancer activity. Prior platinum-based systemic therapy was required, and patients with an EGFR or ALK mutation required appropriately targeted therapy. Napabucasin was administered orally at a starting dose of 240 or 480 mg BID with PTX 80 mg/m2 IV weekly 3 of every 4 weeks. AEs were evaluated using CTCAE v4.03 and objective assessments were performed every 8 weeks per RECIST 1.1. Results: A cohort of 23 pts with advanced non-squamous NSCLC was evaluated. The median number of prior systemic treatment lines was 3, including taxane-based therapy in 100% and immune checkpoint inhibitor in 48% (n = 11). Treatment was well tolerated; related grade 3 AE included diarrhea (n = 4) and fatigue (n = 1). The objective response rate was 26% (6 partial responses [PR]) and the disease control rate (DCR; proportion with SD at 8 weeks plus PR per RECIST) was 70% (n = 16). Tumor regression, including PR, occurred in 35% (n = 8). The median progression-free survival (mPFS) was 5.4 months, and 43% (n = 10) of pts were alive and free of progression at the 24 week time-point or longer. The median overall survival (mOS) was 11.0 months, and 30% (n = 7) of pts were alive for 52 weeks or longer. Conclusions: Clinical safety and encouraging signs of anti-cancer activity were observed in pts with heavily pretreated non-squamous NSCLC who received napabucasin plus weekly paclitaxel. The objective response rate, progression free survival, and overall survival in this population warrant further clinical evaluation and a controlled phase 2/3 trial (CanStem43L) has been initiated. Clinical trial information: NCT01325441.

A phase 1b/2 study of amcasertib, a first-in-class cancer stemness kinase inhibitor, in advanced adenoid cystic carcinoma

6036

Background: Amcasertib (BBI-503) is an oral first-in-class cancer stemness kinase inhibitor. By targeting multiple serine-threonine stemness kinases, amcasertib inhibits Nanog and other cancer stemness pathways. A phase I clinical trial of amcasertib demonstrated safety and signs of anti-cancer activity in patients (pts) with advanced solid tumors. Cancer stemness pathways have been implicated in adenoid cystic carcinoma (ACC). An RP2D expansion cohort was opened for patients with ACC. Methods: Pts with metastatic, unresectable ACC for whom systemic therapy was indicated were enrolled. Amcasertib was administered orally, once or twice daily, in continuous 28-day cycles at a starting dose of 110 mg to 300 mg total daily. Adverse events were categorized according to CTCAE v4.03 and tumor imaging was evaluated per RECIST 1.1 guidelines. Results: 14 pts with ACC were enrolled. Prior treatments included surgery and radiation in all pts (100%), while 57% (n = 8) had received prior systemic therapy (average 2 prior lines, range 1 to 4). Treatment with amcasertib was well tolerated, with grade 3 diarrhea reported in 1 patient and no related grade 4 AEs. The disease control rate (DCR, proportion with stable disease at 8-weeks, partial response, or complete response per RECIST) was 86% (n = 12) with prolonged disease control (≥ 6 months) achieved in 57% (n = 8) patients. At 12 months, 79% of pts were alive. Median overall survival (mOS) was 28.3 months. Conclusions: Clinical safety and encouraging signs of anti-cancer activity were observed in pts with advanced ACC who received treatment with amcasertib. Long term follow-up demonstrates prolonged duration of disease control and that a majority of pts in this cohort have survived beyond 2 years. Further clinical evaluation of amcasertib in pts with ACC is warranted. Clinical trial information: NCT01781455.

Tumor volume score (TVS), modified recist, and tissue damage score (TDS) as novel methods for assessing response in tenosynovial giant cell tumors (TGCT) treated with pexidartinib: Relationship with patient-reported outcomes (PROs)

11048

Background: TGCT is a locally aggressive neoplasm of joint and tendon sheath synovia that may cause pain, limit joint function and destroy bone and local tissues. Measuring TGCT with RECIST is a challenge due to irregular shape and asymmetrical growth, and local tissue damage is not assessed. We reported earlier results of a longitudinal trial of pexidartinib, a selective CSF1R kinase inhibitor, using RECIST as well as novel TVS, modified RECIST and TDS. Here we examine concordance of these MRI measures with PROs. Methods: Patients (pts) with progressive TGCT in a single-arm, multi-center trial of pexidartinib (1000 mg po daily) were assessed by MRI every 2 months by 2 central radiologists (blind to visit order). For RECIST, longest measurable dimensions of up to 2 tumors per joint or tendon sheath were summed (SLD). Modified RECIST summed short axis dimensions (SSD). TVS was based on 10% increments of the estimated maximally distended normal synovial cavity or tendon sheath. TDS scored bone erosion (ERO), cartilage loss (CAR) and bone marrow edema (BME) in multiple regions of each joint. The relationship with PROs (Worst Pain numerical rating scale [NRS] and Worst Stiffness NRS) was assessed. Results: 15 pts (7 knees, 3 hips, 2 ankles, 1 elbow, 1 wrist, 1 thigh) with PRO data and evaluable MRI scans at baseline and Month 7 were assessed. All SLD, SSD and TVS scores improved with respective median changes of -25%, -39% and -50%. Baseline ERO, CAR, and BME ranged 0-19, 0-34, and 0-15, respectively. Median change for each was 0%: ERO worsened in 1 pt, CAR did not change, and BME improved in 4 and worsened in 2. Worst Pain NRS and Worst Stiffness NRS improved in 11 and 9 pts, respectively. Conclusions: TVS demonstrated the greatest pexidartinib effect size, followed by SSD and then conventional RECIST. All had good concordance with PROs. Clinical trial information: NCT01004861. [Table: see text]

A phase 1b/2 study of amcasertib, a first-in-class cancer stemness kinase inhibitor in advanced head and neck cancer

6032

Background: Amcasertib (BBI-503) is an oral first-in-class cancer stemness kinase inhibitor. By targeting multiple serine-threonine stemness kinases, amcasertib inhibits Nanog and other cancer stemness pathways. A phase I clinical trial of amcasertib showed safety and signs of anti-cancer activity in patients (pts) with advanced solid tumors during dose-escalation and RP2D expansion, including pts with advanced head & neck cancer. Methods: Pts with advanced, pre-treated head & neck cancers were enrolled. Amcasertib was administered orally, once or twice daily, in continuous 28-day cycles at a starting dose of 10 mg to 300 mg total daily. Adverse events were categorized according to CTCAE v4.03 and tumor imaging was evaluated per RECIST 1.1 guidelines every 8 weeks. Results: A total of 21 pts were enrolled, 15 with HNSCC and 6 with salivary or parotid gland cancers. Prior treatments included radiation in 90% (19/21), surgery in 71% (15/21) and prior systemic therapy in 90% (19/21, average 3 prior lines, range 1 to 6). Amcasertib was well tolerated with 43% of pts treated at 300 mg daily (n = 9), 33% at 150 mg BID (n = 7), 19% at 200 mg daily (n = 4), and 5% at 10 mg daily (n = 1). Grade 3 AE included diarrhea (n = 4) and nausea (n = 1). Among all patients who received an evaluation per RECIST (n = 16), the objective responses rate (ORR, proportion with partial response [PR] or complete response [CR] per RECIST) was 13% and the disease control rate (DCR, proportion with stable disease [SD] at 8 weeks, PR or CR) was 50%. At 12 months, in the intent-to-treat population (n = 21) 38% of pts were alive. Median overall survival (mOS) of 7.2 months. Conclusions: Clinical safety and encouraging signs of anti-cancer activity were observed in pts with advanced head and neck cancers who have received treatment with amcasertib. Objective response, prolonged disease control, and extended survival have been observed in this pre-treated population with a poor prognosis. Further clinical evaluation of amcasertib in patients with head and neck cancers is warranted. Clinical trial information: NCT01781455.

A phase 1b/2 study of napabucasin with weekly paclitaxel in advanced, previously treated platinum resistant ovarian cancer

5548

Background: Napabucasin is a first-in-class cancer stemness inhibitor, identified by its ability to inhibit STAT3-driven gene transcription and spherogenesis of cancer stem cells (Li et al PNAS 112 (6):1839, 2015). Napabucasin has shown potent synergistic preclinical anti-tumor activity with paclitaxel (PTX). In a phase Ib dose escalation study in patients (pts) with advanced solid tumors, napabucasin plus weekly PTX was well tolerated. A phase II expansion cohort was opened for patients with platinum resistant ovarian cancer. Methods: Pts with advanced ovarian cancer who had disease progression either during or in the 6 months following platinum-based systemic therapy were enrolled. napabucasin was administered orally at a starting dose of 240, 480, or 500 mg twice daily with PTX 80 mg/m2 IV weekly on 3 of every 4 weeks. AEs were evaluated using CTCAE v4.03 and objective assessments were performed per RECIST 1.1 every 8 weeks. Results: A total of 98 pts were enrolled. The average number of prior lines of systemic treatment was 3.5, including prior taxane-based therapy in 100% of patients. Treatment was well tolerated. Related grade 3 adverse events occurring ≥ 5% of pts included diarrhea (12.2%) and vomiting (5.1%). Among pts who received RECIST evaluation (n = 76), the disease control rate (DCR, proportion with SD at 8 weeks + PR + CR) was 65%, and the objective response rate (ORR, PR+CR) was 20%, with complete response in 3 pts (4%). In all patients (ITT, n = 98), the median progression-free survival (mPFS) was 3.0 months and median overall survival (mOS) was 9.3 months. Conclusions: Clinical safety and encouraging signs of anti-cancer activity, including three complete responses, were observed in pts with pre-treated platinum resistant ovarian cancer who received treatment with napabucasin plus weekly PTX. Further clinical evaluation in controlled trials is warranted. Clinical trial information: NCT01325441.

A phase Ib/II study of BBI608 combined with weekly paclitaxel in advanced pancreatic cancer

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Background: Cancer stemness is thought to be associated with resistance to chemotherapies. BBI608, a first-in-class cancer stemness inhibitor that works through inhibiting the Stat3 pathway, has shown potent synergistic anti-tumor activity with paclitaxel in vivo. In a phase Ib dose escalation study in patients with advanced solid tumors, BBI608 plus weekly paclitaxel was well tolerated and a RP2D of BBI608 480 mg BID was determined. Methods: Patients with heavily pretreated metastatic pancreatic adenocarcinoma were enrolled in a phase Ib/II extension study to assess safety, tolerability, and preliminary anti-cancer activity in patients with this diagnosis. BBI608 was administered orally at a starting dose of 480 mg or 500 mg twice daily along with paclitaxel 80 mg/m2 IV weekly 3 of every 4 weeks. A sample size of 40 set the bounds of the 90% CI at ±10% to 14%, assuming a DCR of 60% to 80%. Safety and efficacy results for the cohort will be presented as late breaking data. Results: 41 patients were enrolled. Patients had received a median of 2 prior lines of treatment including FOLFIRINOX (71%), gemcitabine/nab-paclitaxel (44%), or both (37%). Overall, prior therapy included gemcitabine in 90%, a thymidylate synthetase inhibitor (eg 5FU, capecitabine) in 81%, platinum in 76%, irinotecan in 73%, and taxane in 44%. Protocol therapy was well tolerated. Related grade 3 AE included diarrhea (N = 2, 4.9%), abdominal pain (N = 2, 4.9%), and nausea (N = 1, 2.4%), and were rapidly reversible. For evaluable patients (N = 31), response rate (PR+CR) was 7% and disease control rate (SD+PR+CR) was 52%. In evaluable taxane-naïve patients (N = 19), response rate was 11%, disease control rate was 63%, and 16% were progression free at 24 weeks. Overall (ITT, N = 41) mPFS was 10 weeks and mOS was 24 weeks. For the taxane-naïve patients (ITT, N = 23) mPFS was 16 weeks and mOS was 30 weeks. Conclusions: BBI608 plus weekly paclitaxel has demonstrated safety, tolerability, and promising activity in patients with refractory, heavily pretreated pancreatic cancer; particularly in taxane-naïve patients. Durable disease control and prolonged overall survival in this pre-treated population are notable. Clinical trial information: NCT01325441.