NTRK1 Fusions identified by non-invasive plasma next-generation sequencing (NGS) across 9 cancer types

BACKGROUND

Activating fusions of the NTRK1, NTRK2 and NTRK3 genes are drivers of carcinogenesis and proliferation across a broad range of tumour types in both adult and paediatric patients. Recently, the FDA granted tumour-agnostic approvals of TRK inhibitors, larotrectinib and entrectinib, based on significant and durable responses in multiple primary tumour types. Unfortunately, testing rates in clinical practice remain quite low. Adding plasma next-generation sequencing of circulating tumour DNA (ctDNA) to tissue-based testing increases the detection rate of oncogenic drivers and demonstrates high concordance with tissue genotyping. However, the clinical potential of ctDNA analysis to identify NTRK fusion-positive tumours has been largely unexplored.

METHODS

We retrospectively reviewed a ctDNA database in advanced stage solid tumours for NTRK1 fusions.

RESULTS

NTRK1 fusion events, with nine unique fusion partners, were identified in 37 patients. Of the cases for which clinical data were available, 44% had tissue testing for NTRK1 fusions; the NTRK1 fusion detected by ctDNA was confirmed in tissue in 88% of cases. Here, we report for the first time that minimally-invasive plasma NGS can detect NTRK fusions with a high positive predictive value.

CONCLUSION

Plasma ctDNA represents a rapid, non-invasive screening method for this rare genomic target that may improve identification of patients who can benefit from TRK-targeted therapy and potentially identify subsequent on- and off-target resistance mechanisms.

Clinical and Morphologic Characteristics of Extracellular Signal-Regulated Kinase Inhibitor-Associated Retinopathy

PURPOSE

To investigate clinical and morphologic characteristics of serous retinal disturbances in patients taking extracellular signal-regulated kinase (ERK) inhibitors.

DESIGN

Single-center retrospective study of prospectively collected data.

PARTICIPANTS

Of 61 patients receiving ERK inhibitors for treatment of metastatic cancer, this study included 40 eyes of 20 patients with evidence of retinopathy confirmed by OCT.

METHODS

Clinical examination, fundus photography, and OCT were used to evaluate ERK inhibitor retinopathy. The morphologic features, distribution, and location of fluid foci were evaluated serially. Visual acuity (VA) and choroidal thickness measurements were compared at baseline, fluid accumulation, and resolution.

MAIN OUTCOME MEASURES

Characteristics of treatment-emergent choroid and retinal OCT abnormalities as compared with baseline OCT findings and the impact of toxicity on VA.

RESULTS

Of 20 patients with retinopathy, most showed fluid foci that were bilateral (100%), multifocal in each eye (75%), and with at least 1 focus involving the fovea (95%). All subretinal fluid foci occurred between the interdigitation zone and an intact retinal pigment epithelium. No statistical difference was found in choroidal thickness at fluid accumulation and resolution compared with baseline. Forty-five percent of eyes showed evidence of concomitant intraretinal edema localized to the outer nuclear layer. At the time of fluid accumulation, 57.5% eyes showed a decline in VA (mainly by 1-2 lines from baseline). For all eyes with follow-up, the subretinal fluid and intraretinal edema were reversible and resolved without medical intervention, and best-corrected VA at fluid resolution was not statistically different from baseline. Concomitant intraretinal fluid was not associated with worsening of VA. No patient discontinued or decreased drug dose because of retinopathy.

CONCLUSIONS

This study showed that ERK inhibitors may cause subretinal fluid foci with unique clinical and morphologic characteristics. The observed foci were similar to mitogen-activated protein kinase kinase (MEK) inhibitor-associated retinopathy and distinct from central serous chorioretinopathy. However, unlike with MEK inhibitors, an increased occurrence of concomitant intraretinal fluid without significant additive visual impact seems to occur with ERK inhibitors. In this series, ERK inhibitors did not cause irreversible loss of vision or serious eye damage; retinopathy was self-limited and did not require medical intervention.

Abstract P02-02: First results of RLY-4008, a potent and highly selective FGFR2 inhibitor in a first-in-human study in patients with FGFR2-altered cholangiocarcinoma and multiple solid tumors

INTRODUCTION: Oncogenic FGFR2 alterations (fusions/rearrangements, amplifications, mutations) are key drivers in cholangiocarcinoma (CCA) and multiple solid tumors. Current pan-FGFR inhibitor (FGFRi) therapy is limited by off-isoform toxicity and acquired FGFR2 kinase domain resistance mutations. RLY-4008 is a highly selective and potent oral inhibitor designed to target both FGFR2 driver and resistance mutations. We initiated a first-in-human study in advanced solid tumors patients (pts) to define the safety, pharmacokinetics (PK) and efficacy of RLY-4008 (NCT04526106). METHODS: Adult pts received RLY-4008 QD or BID on a 4-week cycle following a BOIN escalation design. Adverse events (AEs), PK, ctDNA and anti-tumor activity (RECIST 1.1) were assessed. RESULTS: As of 16AUG21, 45 pts (35 CCA; 10 other) have been treated with RLY-4008 at total daily doses of 30-200 mg (18 pts BID; 27 pts QD). 44 pts had oncogenic FGFR2 alterations (26 fusions/13 mutations/5 amplifications). The median number of prior anti-neoplastic therapies was 3 (range 1-15). 94% (33/35) of CCA pts had prior chemotherapy and 69% (24/35) had prior FGFRi. 56% (9/16) CCA pts with prior FGFRi and evaluable ctDNA had ≥1 FGFR2 resistance mutation at baseline, most commonly at positions 549 (8/9), 617 (3/9), or 564 (2/9). RLY-4008 had rapid absorption (Tmax 1-7h), half-life to support QD dosing (18-34 h), dose-dependent exposure (AUC; Cmax) and predicted FGFR2 occupancy >85% across dose levels. The MTD has not been defined, and QD dose exploration continues to select the optimal biologically efficacious dose. AEs occurring in >20% of pts include stomatitis (49%), palmar-plantar erythrodysesthesia (PPE, 38%), dry mouth (29%), and nail toxicities (22%), majority of which were ≤Gr 2. 6 pts had Gr 1-2 retinopathy, which resolved in all cases. 5 AEs were considered dose limiting toxicities: 4 in BID (rash/PPE/mucositis/hyperbilirubinemia) and 1 in QD (retinopathy). No Gr 4/5 drug-related AEs were seen. 25 pts remain on treatment (range 1-37 weeks). RLY-4008 showed broad anti-tumor activity across dose levels and FGFR2 alterations with radiographic tumor reductions of ≥10% in 59% pts (19/32; -11% to -83%). Activity was seen in FGFRi-naïve, FGFR2-fusion+ CCA with PRs in 50% of pts (3/6, 2 confirmed and 1 pending confirmation; -56% to -83%). Activity was also seen in FGFRi pre-treated FGFR2-fusion+ CCA pts (N=16) with 16 SD, including 9 pts with tumor reduction ≥10% (from -12% to -35%). Of the FGFRi pre-treated FGFR2-fusion+ CCA patients with detectable FGFR2 resistance mutations in ctDNA at baseline, 78% (7/9) were undetectable at C2D1. CONCLUSION: RLY-4008 demonstrates promising safety, tolerability, and clinical activity in FGFR2-altered solid tumor pts, including those who progressed on prior FGFRi therapy. Consistent with the FGFR2-selective mechanism, minimal off-isoform toxicity (FGFR1-hyperphosphatemia; FGFR4-diarrhea) was seen. These encouraging data validate selective targeting of FGFR2 and suggest that RLY-4008 has potential to overcome resistance to FGFRi.

Citation Format: Lipika Goyal, Mitesh Borad, Vivek Subbiah, Amit Mahipal, Suneel Kamath, Kabir Mody, Robin Katie Kelley, Richard Kim, Vaibhav Sahai, Anthony El-Khoueiry, Efrat Dotan, Oleg Schmidt-Kittler, Jinshan Shen, Kai Yu Jen, Alicia Deary, Wei Guo, Mahesh Padval, Cori Ann J. Sherwin, Charles Ferte, Beni Wolf, Alison M. Schram. First results of RLY-4008, a potent and highly selective FGFR2 inhibitor in a first-in-human study in patients with FGFR2-altered cholangiocarcinoma and multiple solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P02-02.

Clinical and Morphologic Characteristics of Fibroblast Growth Factor Receptor Inhibitor-Associated Retinopathy

Importance

Fibroblast growth factor receptor (FGFR) 1 to 4 inhibitors are approved by the US Food and Drug Administration and suppress the mitogen-activated protein kinase (MAPK) pathway, with a potential for treatment-related retinopathy. To date, implications of FGFR inhibitor-associated ocular toxic effects are poorly described. Therefore, more detailed clinical descriptions of this ocular toxic effect could help explain visual symptoms while receiving drug therapy.

Objective

To describe the clinical and morphologic characteristics of serous retinal disturbances associated with FGFR inhibitors.

Design, Setting, and Participants

In this retrospective case series, 146 patients receiving FGFR inhibitors as cancer treatment at a single tertiary referral center were included. This study included 40 eyes of 20 patients with retinopathy by optical coherence tomography (OCT). OCTs were obtained on the remaining patients and the results were judged normal. Patients were recruited from March 2012 to January 2021.

Main Outcomes and Measures

Characteristics of treatment-emergent choroidal and retinal OCT abnormalities as compared with baseline OCT, associated with visual acuity at presentation and at fluid resolution.

Results

A total of 20 of 146 patients (13.7%) exhibited FGFR inhibitor-associated retinopathy. Of these 20 patients, 11 (55%) were female, and the median (range) age was 62.6 (42.7-86.0) years. The median (range; mean) time from medication start to initial subretinal fluid detection was 21 (5-125; 32) days. The median (interquartile range [IQR]) baseline logMAR best-corrected visual acuity (BCVA) was 0 (0-0.1). At fluid accumulation, 11 eyes had decreased vision: the median (IQR) subgroup baseline BCVA was 0 (0-0.1); and the median (IQR) BCVA change from baseline to accumulation was -0.1 (-0.2 to -0.1). For 26 eyes (65%) with follow-up, the subretinal fluid resolved without medical intervention or drug interruption in all but 1 patient. At fluid resolution, the median (IQR) BCVA was 0.1 (0-0.1), and the change in median (IQR) BCVA from baseline to fluid resolution was 0 (-0.03 to 0). No patient discontinued drug therapy on account of their retinopathy.

Conclusions and Relevance

FGFR inhibitors result in subretinal fluid foci similar to other drugs that inhibit the MAPK pathway. In this series, FGFR inhibitors did not cause irreversible loss of vision; the retinopathy was self-limited and did not require medical intervention. These results may explain visual symptoms while taking the drug, although the precise frequency or magnitude of this adverse effect cannot be determined with certainty from this retrospective investigation.

Spectrum of BRAF Mutations and Gene Rearrangements in Ovarian Serous Carcinoma

Low-grade serous carcinoma (LGSC) is a rare type of ovarian cancer, which commonly arises from serous borderline tumor (SBT) and is characterized by frequent activating mutations in the mitogen-activated protein kinase pathway, including BRAF. The BRAF ^V600E mutation is associated with improved prognosis in SBT and LGSC, and responses to BRAF inhibitor therapy have been reported. We sought to characterize the clinicopathologic and molecular features of BRAF-driven tubo-ovarian and primary peritoneal serous tumors.

METHODS

Retrospective analysis of our institutional cohort of SBTs (n = 22), LGSCs (n = 119) and high-grade serous carcinomas (HGSCs, n = 1,290) subjected to targeted massively parallel sequencing was performed to identify cases with BRAF genetic alterations. Putative BRAF rearrangements were confirmed using targeted RNA sequencing and/or fluorescence in situ hybridization (FISH). BRAF^V600E oncoprotein expression was assessed by immunohistochemistry on selected cases.

RESULTS

BRAF somatic genetic alterations were identified in 29 of 1,431 (2%) serous tumors and included mutations (n = 24), gene rearrangements (n = 3), and amplification (n = 2). BRAF mutations were more frequent in SBTs (7 of 22; 32%) compared with LGSCs (11 of 119; 9%, P = .009) and HGSCs (6 of 1,290; 0.5%; P < .0001, SBT/LGSC v HGSC). The BRAF ^V600E hotspot mutation was most common (n = 16); however, other BRAF driver mutations were also detected (n = 8). BRAF mutations were often clonal or truncal in SBTs and LGSCs, but subclonal in most HGSCs. Pathogenic BRAF gene fusions were identified in LGSCs (n = 2) and HGSC (n = 1) and involved distinct fusion partners (AGK, MKRN1, and AGAP3). Three patients with BRAF-mutant LGSC were treated with targeted mitogen-activated protein kinase inhibitors, one of whom was maintained on therapy for over 3 years with clinical benefit.

CONCLUSION

Recognition of BRAF alterations beyond V600E mutation in LGSC may have clinical implications for appropriate targeted therapy selection.

Clinicopathologic Features and Response to Therapy of NRG1 Fusion-Driven Lung Cancers: The eNRGy1 Global Multicenter Registry

PURPOSE

Although NRG1 fusions are oncogenic drivers across multiple tumor types including lung cancers, these are difficult to study because of their rarity. The global eNRGy1 registry was thus established to characterize NRG1 fusion-positive lung cancers in the largest and most diverse series to date.

METHODS

From June 2018 to February 2020, a consortium of 22 centers from nine countries in Europe, Asia, and the United States contributed data from patients with pathologically confirmed NRG1 fusion-positive lung cancers. Profiling included DNA-based and/or RNA-based next-generation sequencing and fluorescence in situ hybridization. Anonymized clinical, pathologic, molecular, and response (RECIST v1.1) data were centrally curated and analyzed.

RESULTS

Although the typified never smoking (57%), mucinous adenocarcinoma (57%), and nonmetastatic (71%) phenotype predominated in 110 patients with NRG1 fusion-positive lung cancer, further diversity, including in smoking history (43%) and histology (43% nonmucinous and 6% nonadenocarcinoma), was elucidated. RNA-based testing identified most fusions (74%). Molecularly, six (of 18) novel 5' partners, 20 unique epidermal growth factor domain-inclusive chimeric events, and heterogeneous 5'/3' breakpoints were found. Platinum-doublet and taxane-based (post-platinum-doublet) chemotherapy achieved low objective response rates (ORRs 13% and 14%, respectively) and modest progression-free survival medians (PFS 5.8 and 4.0 months, respectively). Consistent with a low programmed death ligand-1 expressing (28%) and low tumor mutational burden (median: 0.9 mutations/megabase) immunophenotype, the activity of chemoimmunotherapy and single-agent immunotherapy was poor (ORR 0%/PFS 3.3 months and ORR 20%/PFS 3.6 months, respectively). Afatinib achieved an ORR of 25%, not contingent on fusion type, and a 2.8-month median PFS.

CONCLUSION

NRG1 fusion-positive lung cancers were molecularly, pathologically, and clinically more heterogeneous than previously recognized. The activity of cytotoxic, immune, and targeted therapies was disappointing. Further research examining NRG1-rearranged tumor biology is needed to develop new therapeutic strategies.

Comprehensive Molecular and Clinicopathologic Analysis of 200 Pulmonary Invasive Mucinous Adenocarcinomas Identifies Distinct Characteristics of Molecular Subtypes

PURPOSE

Invasive mucinous adenocarcinoma (IMA) is a unique subtype of lung adenocarcinoma, characterized genomically by frequent KRAS mutations or specific gene fusions, most commonly involving NRG1. Comprehensive analysis of a large series of IMAs using broad DNA- and RNA-sequencing methods is still lacking, and it remains unclear whether molecular subtypes of IMA differ clinicopathologically.

EXPERIMENTAL DESIGN

A total of 200 IMAs were analyzed by 410-gene DNA next-generation sequencing (MSK-IMPACT; n = 136) or hotspot 8-oncogene genotyping (n = 64). Driver-negative cases were further analyzed by 62-gene RNA sequencing (MSK-Fusion) and those lacking fusions were further tested by whole-exome sequencing and whole-transcriptome sequencing (WTS).

RESULTS

Combined MSK-IMPACT and MSK-Fusion testing identified mutually exclusive driver alterations in 96% of IMAs, including KRAS mutations (76%), NRG1 fusions (7%), ERBB2 alterations (6%), and other less common events. In addition, WTS identified a novel NRG2 fusion (F11R-NRG2). Overall, targetable gene fusions were identified in 51% of KRAS wild-type IMAs, leading to durable responses to targeted therapy in some patients. Compared with KRAS-mutant IMAs, NRG1-rearranged tumors exhibited several more aggressive characteristics, including worse recurrence-free survival (P < 0.0001).

CONCLUSIONS

This is the largest molecular study of IMAs to date, where we demonstrate the presence of a major oncogenic driver in nearly all cases. This study is the first to document more aggressive characteristics of NRG1-rearranged IMAs, ERBB2 as the third most common alteration, and a novel NRG2 fusion in these tumors. Comprehensive molecular testing of KRAS wild-type IMAs that includes fusion testing is essential, given the high prevalence of alterations with established and investigational targeted therapies in this subset.

Abstract 956: The HER2×HER3 bi-specific antibody Zenocutuzumab is effective at blocking growth of tumors driven by NRG1 gene fusions

Fusions involving the neuregulin 1 gene (NRG1) occur at low frequency in pancreatic, lung, and other cancers. NRG1 fusion oncoproteins bind to HER3, leading to heterodimerization with HER2 and potent activation of downstream signaling mainly via the PI3K-AKT pathway. Zenocutuzumab (Zeno, MCLA-128), an ADCC-enhanced anti-HER2×HER3 bi-specific antibody, uniquely ‘docks' on HER2, to position the antibody and subsequently ‘block' NRG1 from interacting with HER3, effectively preventing HER2:HER3 heterodimerization and downstream signaling. Our goal in this study was to evaluate the efficacy of Zeno in preclinical models of NRG1 fusion-positive cancers.

We tested Zeno in a panel of isogenic and patient-derived cell line and xenograft (PDX) models of lung, breast and pancreatic cancers. Cell lines either expressed an NRG1 fusion endogenously (MDA-MB-175-VII, DOC4-NRG1) or by lentiviral transfer of cDNAs (ATP1B1-NRG1 and SLC3A2-NRG1 in H6c7 pancreatic ductal cell line; CD74-NRG1 and VAMP2-NRG1 in immortalized human bronchial epithelial cells; and DOC4-NRG1 in MCF7 breast cancer cells). PDX models were generated from NSCLC samples harboring CD74-NRG1 (ST3204) or SLC3A2-NRG1 (LUAD-0061AS3) fusions and from a high grade serous ovarian cancer harboring a CLU-NRG1 fusion (OV-10-0050). Zeno treatment of NRG1 fusion-expressing breast, pancreatic, and lung cancer cell lines resulted in dose-dependent reduction of growth and abrogated phosphorylation of HER3, HER4, AKT, p70S6 kinase and STAT3 in all cell lines tested. Phosphorylation of HER2, EGFR and MEK/ERK was inhibited, albeit with some variation, in a cell line-specific manner. Growth of isogenic control cell lines without NRG1 fusion was not significantly altered. In breast and lung cancer cell lines, Zeno treatment down-regulated cyclin D1 expression and induced expression of the negative cell cycle regulators P21 or P27. Evidence of apoptosis activation (cleaved PARP, expression of BIM and PUMA) was also observed in cells exposed to Zeno. Treatment of mice bearing LUAD-0061AS3, ST3204 and OV-10-0050 PDX tumors (2.5, 8, 25 mg/kg, QW) caused a dose-dependent inhibition of tumor growth, with tumor shrinkage observed at higher doses. Finally, we assessed the ability of Zeno to induce antibody-dependent cellular cytotoxicity using a chromium release assay and peripheral blood mononuclear cells. Zeno induced significant cytotoxicity in MDA-MB-175-VII cells while a non-ADCC enhanced, non-specific IgG had no effect.

Here we show that Zeno effectively blocks the growth of NRG1 fusion-positive cell line and xenograft models of tumors arising from lung, pancreas and other organs, and these results support the continued development of Zeno to treat patients with this molecularly defined subset of cancers.

Citation Format: Igor Odintsov, Inna Khodos, Madelyn Espinosa-Cotton, Allan J. Lui, Marissa Mattar, Alison M. Schram, Ron C. Schackmann, Jeroen Lammerts van Bueren, Cecile A. Geuijen, Elisa de Stanchina, Marc Ladanyi, Romel Somwar. The HER2×HER3 bi-specific antibody Zenocutuzumab is effective at blocking growth of tumors driven by NRG1 gene fusions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 956.

First-in-human study of highly selective FGFR2 inhibitor, RLY-4008, in patients with intrahepatic cholangiocarcinoma and other advanced solid tumors

TPS4165

Background: Oncogenic activation of FGFR2 via genomic rearrangement, gene amplification, or point mutation in advanced solid tumors provides the opportunity for rapid clinical development of highly selective FGFR2 inhibitors using a precision oncology approach to deliver clinical benefit to genomically-defined patient (pt) populations. Unfortunately, this opportunity remains largely unrealized as current, non-selective small molecule inhibitors (pan-FGFRi) suffer from off-isoform toxicity (FGFR1-hyperphosphatemia; FGFR4-diarrhea) and on-target acquired resistance leading to only modest efficacy primarily limited to FGFR2-fusion+ intrahepatic cholangiocarcinoma (ICC). RLY-4008 is a novel, oral FGFR2 inhibitor designed to overcome the limitations of pan-FGFRi by potently and selectively targeting primary oncogenic FGFR2 alterations and acquired resistance mutations. We initiated a first-in-human (FIH) precision oncology study of RLY-4008 in advanced solid tumor pts with FGFR2 alterations with primary objectives to define the maximum tolerated dose/recommended phase 2 dose (MTD/RP2D) and adverse event (AE) profile of RLY-4008 and key secondary objectives to assess FGFR2 genotype in blood and tumor tissue, pharmacokinetics (PK), and anti-tumor activity. Methods: This is a global, multi-center, FIH dose escalation/expansion study of RLY-4008 (NCT04526106) in adult pts who have unresectable or metastatic solid tumors with FGFR2 alteration per local assessment, ECOG performance status 0-2, measurable or evaluable disease per RECIST 1.1, and who are refractory, intolerant, or declined standard therapy including pan-FGFRi. FGFR2 alteration will be confirmed retrospectively by central laboratory assessment. For the dose escalation (Ñ50), RLY-4008 is administered QD/BID on a continuous schedule with 4-week cycles according to a Bayesian Optimal Interval design that allows accelerated dose titration, additional accrual to dose levels declared tolerable, and exploration of alternative schedules if warranted. The MTD is determined via logistic regression of the dose limiting toxicity rate across all dose levels and an RP2D less than the MTD may be considered based on observed AEs, PK, and anti-tumor activity. Following dose escalation, the dose expansion (Ñ75) will treat pts with RLY-4008 at the MTD/RP2D and includes 5 groups with any prior therapy (except group 2): 1. FGFR2 fusion+ ICC pts; 2. FGFR2 fusion+ ICC pts with no prior FGFRi; 3. FGFR2 fusion+ pts with other solid tumors; 4. FGFR2-mutation+ solid tumor pts and 5. FGFR2-amplified solid tumor pts. The primary endpoints are MTD/RP2D and AE profile; key secondary endpoints are FGFR2 genotype in blood and tumor tissue, PK parameters; overall response rate, and duration of response per RECIST 1.1. US enrollment began SEP2020 and Europe/Asia start-up is underway. Clinical trial information: NCT04526106.

Clinical pharmacokinetics of bdtx-189, an inhibitor of allosteric ErbB mutations, in patients with advanced solid malignancies in MasterKey-01 study

3097

Background: Allosteric oncogenic mutations occur outside the canonical ATP-binding site of EGFR and HER2, and there are no approved therapies that target such mutations. BDTX-189 is a potent, selective, irreversible inhibitor of 48 allosteric EGFR and HER2 mutant variants under clinical evaluation in the ongoing MasterKey-01 trial (NCT04209465). BDTX-189 was designed to rapidly and irreversibly occupy the active site of targeted ErbB mutants, leading to sustained pharmacodynamic (PD) effects, and with selectivity over EGFR-WT in order to minimize EGFR-WT mediated toxicities. The pharmacokinetic (PK) profile was designed for rapid absorption and fast elimination to maintain target occupancy while minimizing prolonged drug exposure that could contribute to off-target associated toxicities. Methods: In MasterKey-01, BDTX-189 was administered orally once daily in continuous 21-day cycles, taken fasted. Dose escalation included cohorts of 1-2 patients receiving doses between 25 and 200 mg QD followed by 5-7 patients receiving 400 mg, 800 mg, or 1,200 mg QD fasted. The possible effects of a high fat meal on the PK of BDTX-189 were assessed in a subset of patients receiving single doses of 400 mg BDTX-189 fasted and immediately after a high-fat breakfast in a randomized crossover fashion with 3 days between doses. In addition, a dose escalation cohort investigating administration of BDTX-189 non-fasted was enrolled at 800 mg QD. Serial blood samples for analysis of plasma BDTX-189 concentrations were collected after each dose on C1D1 and C1D15. BDTX-189 levels were determined using LC-MS, and data analyzed using non-compartmental methods. Results: After single and multiple doses, BDTX-189 was rapidly absorbed (median tmax 1-2 h), with an elimination t1/2 of 2-6 h. Dose-dependent increases in exposure from 200 to 800 mg QD fasted were observed, with no apparent accumulation or decline in exposures observed at steady-state. Administration of BDTX-189 with a high-fat meal increased AUC approximately 1.7-fold with minimal effect on Cmax, relative to administration in the fasted state. At 800 mg QD, mean AUC was similar in the non-fasting state relative to fasting and was within the target efficacious range defined by mouse models harboring allo-ErbB mutated tumors. Median tmax and t1/2 values were similar after administration in the non-fasted and fasted states. Conclusions: BDTX-189 demonstrated rapid absorption and a short PK half-life consistent with the desired PK/PD profile, with exposures in the efficacious target range based on preclinical data. The pilot high fat food-effect data and non-fasting QD dosing regimen show similar or improved systemic exposure relative to dosing in the fasted state. The MasterKey-01 trial is ongoing, including refinement of the dosing regimen and identification of the recommended phase 2 dose. Clinical trial information: NCT04209465.

BRCA reversion mutations in a pan-cancer cohort to reveal BRCA-dependence in select noncanonical BRCA-mutant histologies

3012

Background: Loss of BRCA1/2 function leads to homologous recombination deficiency (HRD) and can enhance platinum and PARP inhibitor sensitivity in breast, pancreas, prostate, and ovarian cancers. In BRCA-associated cancers, resistance can result from the development of BRCA1/2 reversion mutations, which restore BRCA1/2 function. By contrast, a BRCA mutation may be an incidental finding in other tumor histologies. Methods: To determine the distribution of reversion mutations in a pan-cancer cohort, the MSK-IMPACT clinical sequencing cohort was mined to identify patients who had both a germline BRCA1/2 mutation and a frameshift somatic reversion mutation that restored BRCA1/2 function. Whole exome resequencing was used to detect HRD signatures. Chart review enabled collection of data on treatment history in patients consented to germline testing. Results: Of the 33,277 patients with matched tumor and normal sequencing profiled in this study, 861 patients were found to have germline pathogenic BRCA1/2 alterations, including 347 (40%) in BRCA1 and 514 (60%) in BRCA2. Somatic BRCA1/2 driver alterations were also found in tumor tissue from an additional 447 patients, with 156 (35%) having BRCA1 mutations, and the remainder having alterations in BRCA2 (65%) . Among the 1,308 germline or somatic BRCA1/2 mutant tumors, we identified reversion mutations in 12 patients, all of whom were germline carriers of BRCA1/2, comprising 3 BRCA1 and 9 BRCA2 tumors. 7 patients consented to germline testing enabling review of clinical characteristics and treatment history, 5 of whom received PARP inhibitor or platinum-therapy prior to reversion detection. Ten of 12 tumors with reversion mutations were in canonical BRCA-associated cancers. Interestingly, reversion mutations were also found in patients with lung adenocarcinoma (n=1) and gastroesophageal junction adenocarcinoma (n=1). In both these non-canonical histologies, the reversion was detected following progression on platinum-based therapy. Whole exome resequencing of the lung tumor revealed the classic somatic molecular phenotypes of HRD that are characteristic of BRCA-dependent tumors, including in terms of large-scale transitions, HRD-loss of heterozygosity, signature 3, and the number of telomeric allelic imbalance score. Conclusions: Matched tumor and normal sequencing from a large cohort of patients with diverse cancer histologies reveals that reversion mutations are found across BRCA-associated cancer types. In rare cases, reversion mutations in BRCA1/2 following platinum-based therapy may be indicative of prior BRCA-dependence in select non-canonical tumor histologies.

Efficacy and safety of zenocutuzumab in advanced pancreas cancer and other solid tumors harboring NRG1 fusions

3003

Background: NRG1 fusion proteins are oncogenic drivers in pancreas cancer and other solid tumors. They bind HER3, leading to HER2/HER3 heterodimerization and oncogenic transformation. The activity of zenocutuzumab (MCLA-128; zeno), a bispecific antibody targeting NRG1 fusion signaling in NRG1 fusion positive ( NRG1+) cancers, is being evaluated in the ongoing global multicenter phase 2 part of the eNRGy study and a global early access program (EAP). Methods: Enrolled patients (pts) have advanced NRG1+ pancreas cancer, non-small cell lung cancer (NSCLC), and other solid tumors previously treated with standard therapy, are ≥ 18 years-old, have ECOG ≤1, adequate organ function, and measurable disease (RECIST v1.1). Zeno dosing: 750 mg IV every 2 weeks until progression or unacceptable toxicity. Primary endpoint: investigator (INV)-assessed objective response rate (ORR). Secondary endpoints: ORR per central independent radiologist review, duration of response (DOR), and safety. Tumor imaging is conducted every 8 weeks. Results: 51 pts with NRG1+ cancer have received zeno, 37 in the eNRGy study and 14 pts in the EAP. As of 12 Jan 2021, treatment is ongoing in 27/51 pts (8/13 pancreas, 10/25 NSCLC, 9/13 other solid tumors). Among the 51 pts, 10 pts with pancreas cancer, 18 pts with NSCLC, and 5 pts with other solid tumors had measurable disease and had the opportunity for ≥1 tumor assessment (TA) and are included in this analysis. Among the 10 pts with pancreas cancer, median age was 49 y (range 34-72), 50% were male, 6/4 pts had ECOG 0/1, and all had metastatic disease and were KRAS wild-type. The median number of prior therapies was 3 (range 1-6). The INV-assessed confirmed ORR was 40% (4/10; 90% CI, 15;70), and for this cohort of pts, responses occurred at the first TA. Tumor regression was seen in 7/10 pts, and the disease control rate was 90% (90% CI, 61-100). A CA 19-9 decline of ≥ 50% was observed in 9/9 (100%) pts. DOR is pending. In the overall NRG1+ population, tumor regression was observed in 25 of 33 pts and confirmed INV-assessed responses were seen in 9 of 33 pts (ORR 27%; 90% CI, 15;43), including in pts who previously received afatinib. Zeno was well tolerated with no pts requiring dose reduction for toxicity. Across all cohorts, for individual AEs, grade 3 events were reported in ≤5% of pts, and there was a notable lack of cardiotoxicity and severe gastrointestinal or skin toxicity. Updated data from all cohorts (pancreas, NSCLC, other solid tumors) will be presented. Conclusions: Zeno induces rapid and major radiologic tumor regression and biomarker responses in heavily-pretreated metastatic KRAS wild-type NRG1+ pancreas cancer, with minimal toxicity. Zeno is a promising novel targeted therapeutic option for pts with NRG1+ cancers. Clinical trial information: NCT02912949.

Safety and preliminary efficacy from the phase 1 portion of MasterKey-01: A First-in-human dose-escalation study to determine the recommended phase 2 dose (RP2D), pharmacokinetics (PK) and preliminary antitumor activity of BDTX-189, an inhibitor of allosteric ErbB mutations, in patients (pts) with advanced solid malignancies

3086

Background: BDTX-189 is an orally available, ATP-competitive and irreversible inhibitor directed against families of allosteric HER2 and EGFR oncogenic mutations. In preclinical studies BDTX-189 achieved potent inhibition of 48 allosteric HER2 and EGFR/HER2 exon 20 insertion mutant variants with selectivity versus EGFR wild-type (WT) and demonstrated tumor growth inhibition and regression in vivo. The primary objective of the Ph 1 portion of this trial (NCT04209465) is to determine the RP2D and schedule of monotherapy BDTX-189 in pts with advanced solid tumors. Methods: Eligibility includes pts with relapsed or refractory locally advanced or metastatic solid tumors with no standard therapy available whose tumor harbors an allosteric HER2 or HER3 mutation; EGFR or HER2 exon 20 insertion mutation; HER2 amplification or overexpression; or EGFR exon 19 deletion or L858R mutation. BDTX-189 is dosed continuously orally in 3-wk cycles QD and BID in separate dose escalation cohorts. A separate cohort is also evaluating the high- and low-fat food-effect (FE) on BDTX-189 PK. Results: As of 1/11/21, 46 pts have been dosed, with 36 in the QD (fasting) schedule (25-1200 mg), including pts from the FE cohort who received 800 mg QD fasting after FE evaluation: 58% female; 67% white; median age 63.5 yrs; 53% received ≥ 3 prior tx lines. Cancer types: 12 NSCLC, 5 breast, 4 ovary, 3 biliary, and 12 other. Genomic alterations: 23 HER2 amplification and the following mutations: 11 allosteric HER2, 5 EGFR exon 20 insertion, 5 HER2 exon 20 insertion, 3 EGFR exon 19 del./L858R, and 2 HER3. At ≥ 800 mg QD, 3 and 2 pts had EGFR or HER2 exon 20 mutations, respectively. The maximum tolerated dose (MTD) for QD (fasting) was 800 mg, with 2/6 pts with DLTs at 1200 mg. DLTs: gastrointestinal (G3 diarrhea; G1/2 nausea/vomiting). The most frequent (≥20%) related adverse events were diarrhea (36%, 8% G3), nausea (28%, 0% G3), and vomiting (25%, 3% G3). The rate of skin disorders was 11% with the highest severity of G2 in 1 pt. Dose-dependent exposure increases were observed, with the exposure at 800 mg QD fasting within the projected efficacious range. Pilot FE data suggest possible increased exposure with food. 27 pts were evaluable for efficacy, 15 at ≥ 800 mg QD, with 2 partial responses observed: 1 PR confirmed and ongoing (800 mg QD, CUP, HER2 amp, 3 prior lines of chemo) and 1 PR unconfirmed (NSCLC with brain mets, 1200 mg QD, HER2 amp + exon 19 del., 2 prior EGFR TKIs). 3 pts had a best response of SD and 10 with progressive disease. Conclusions: BDTX-189 has a generally manageable safety profile with early evidence of anti-tumor activity. Enrollment is ongoing in non-fasting QD and BID cohorts, and the FE cohort, prior to RP2D identification. Clinical trial information: NCT04209465.

COVID-19 vaccine guidance for patients with cancer participating in oncology clinical trials

Emerging efficacy data have led to the emergency use authorization or approval of COVID-19 vaccines in several countries worldwide. Most trials of COVID-19 vaccines excluded patients with active malignancies, and thus data on the safety, tolerability and efficacy of the vaccines in patients with cancer are currently limited. Given the risk posed by the COVID-19 pandemic, decisions regarding the use of vaccines against COVID-19 in patients participating in trials of investigational anticancer therapies need to be addressed promptly. Patients should not have to choose between enrolling on oncology clinical trials and receiving a COVID-19 vaccine. Clinical trial sponsors, investigators and treating physicians need operational guidance on COVID-19 vaccination for patients with cancer who are currently enrolled or might seek to enrol in clinical trials. Considering the high morbidity and mortality from COVID-19 in patients with cancer, the benefits of vaccination are likely to far outweigh the risks of vaccine-related adverse events. Herein, we provide operational COVID-19 vaccine guidance for patients participating in oncology clinical trials. In our perspective, continued quality oncological care requires that patients with cancer, including those involved in trials, be prioritized for COVID-19 vaccination, which should not affect trial eligibility.

IgE blockade with omalizumab reduces pruritus related to immune checkpoint inhibitors and anti-HER2 therapies

Background:

Immunoglobulin E (IgE) blockade with omalizumab has demonstrated clinical benefit in pruritus-associated dermatoses (e.g. atopic dermatitis, bullous pemphigoid, urticaria). In oncology, pruritus-associated cutaneous adverse events (paCAEs) are frequent with immune checkpoint inhibitors (CPIs) and targeted anti-human epidermal growth factor receptor 2 (HER2) therapies. Thus, we sought to evaluate the efficacy and safety of IgE blockade with omalizumab in cancer patients with refractory paCAEs related to CPIs and anti-HER2 agents.

Patients and methods:

Patients included in this multicenter retrospective analysis received monthly subcutaneous injections of omalizumab for CPI or anti-HER2 therapy-related grade 2/3 pruritus that was refractory to topical corticosteroids plus at least one additional systemic intervention. To assess clinical response to omalizumab, we used the Common Terminology Criteria for Adverse Events version 5.0. The primary endpoint was defined as reduction in the severity of paCAEs to grade 1/0.

Results:

A total of 34 patients (50% female, median age 67.5 years) received omalizumab for cancer therapy-related paCAEs (71% CPIs; 29% anti-HER2). All had solid tumors (29% breast, 29% genitourinary, 15% lung, 26% other), and most (n = 18, 64%) presented with an urticarial phenotype. In total, 28 of 34 (82%) patients responded to omalizumab. The proportion of patients receiving oral corticosteroids as supportive treatment for management of paCAEs decreased with IgE blockade, from 50% to 9% (P < 0.001). Ten of 32 (31%) patients had interruption of oncologic therapy due to skin toxicity; four of six (67%) were successfully rechallenged following omalizumab. There were no reports of anaphylaxis or hypersensitivity reactions related to omalizumab.

Conclusions:

IgE blockade with omalizumab demonstrated clinical efficacy and was well tolerated in cancer patients with pruritus related to CPIs and anti-HER2 therapies.

TRK xDFG Mutations Trigger a Sensitivity Switch from Type I to II Kinase Inhibitors

On-target resistance to next-generation TRK inhibitors in TRK fusion-positive cancers is largely uncharacterized. In patients with these tumors, we found that TRK xDFG mutations confer resistance to type I next-generation TRK inhibitors designed to maintain potency against several kinase domain mutations. Computational modeling and biochemical assays showed that TRKA^G667 and TRKC^G696 xDFG substitutions reduce drug binding by generating steric hindrance. Concurrently, these mutations stabilize the inactive (DFG-out) conformations of the kinases, thus sensitizing these kinases to type II TRK inhibitors. Consistently, type II inhibitors impede the growth and TRK-mediated signaling of xDFG-mutant isogenic and patient-derived models. Collectively, these data demonstrate that adaptive conformational resistance can be abrogated by shifting kinase engagement modes. Given the prior identification of paralogous xDFG resistance mutations in other oncogene-addicted cancers, these findings provide insights into rational type II drug design by leveraging inhibitor class affinity switching to address recalcitrant resistant alterations. SIGNIFICANCE: In TRK fusion-positive cancers, TRK xDFG substitutions represent a shared liability for type I TRK inhibitors. In contrast, they represent a potential biomarker of type II TRK inhibitor activity. As all currently available type II agents are multikinase inhibitors, rational drug design should focus on selective type II inhibitor creation.This article is highlighted in the In This Issue feature, p. 1.

Clinical implications of drug-induced liver injury in early-phase oncology clinical trials

BACKGROUND

Data on drug-induced liver injury (DILI) and acute liver failure (ALF) in modern phase 1 oncology trials are limited, specifically with respect to the incidence and resolution of DILI and the safety of drug rechallenge.

METHODS

This study reviewed all patients who were recruited to phase 1 oncology trials between 2013 and 2017 at Memorial Sloan Kettering Cancer Center. Clinicopathologic data were extracted to characterize DILI, and attribution was assessed on the basis of data prospectively generated during the studies. Logistic regression models were used to explore factors related to DILI and DILI recurrence after drug rechallenge.

RESULTS

Among 1670 cases recruited to 85 phase 1 trials, 81 (4.9%) developed DILI. The rate of DILI occurrence was similar for patients in immune-based trials and patients in targeted therapy trials (5.0% vs 4.9%), as was the median time to DILI (5.5 vs 6.5 weeks; P = .48). Two patients (0.12%) met the criteria of Hy's law, although none developed ALF. The DILI resolved in 96% of the patients. Pretreatment factors were not predictive for DILI development. Thirty-six of the 81 patients underwent a drug rechallenge, and 28% of these patients developed DILI recurrence. Peak alanine aminotransferase during the initial DILI was associated with DILI recurrence (odds ratio, 1.04; 95% confidence interval, 1.0-1.09; P = .035).

CONCLUSIONS

In modern phase 1 oncology trials, DILI is uncommon, may occur at any time, and often resolves with supportive measures. Rechallenging after DILI is feasible; however, the high rate of DILI recurrence suggests that clinicians should consider the severity of the DILI episode and treatment alternatives.

Abstract 5280: Kinase fusions drive endocrine resistance in estrogen receptor-positive breast cancer

Oncogenic kinase activation by gene fusions can promote cancer development and tumor progression, however, kinase fusions have not been characterized extensively in breast cancer. In this study, we characterized kinase fusions in a large cohort of 4854 breast cancer patients using clinical DNA and/or RNA next generation sequencing platforms. Twenty-seven cases harboring kinase fusions were identified, including 11 FGFR (5 FGFR2, 3 FGFR3, 3 FGFR1), 5 BRAF, 4 NTRK1, 2 RET, 2 ROS1, 1 ALK, 1 ERBB2, and 1 MET. Eight patients with a history of endocrine therapy had available pre-treatment samples, of which six were negative for kinase fusion, and ESR1 hotspot mutations were not observed in any of these kinase fusion-positive samples. These findings suggest a potential role for kinase fusions in endocrine therapy resistance and prompted us to model the kinase fusions in human breast cancer cell lines. Ectopic expression of LMNA-NTRK1 fusion kinase activated growth factor signaling cascades, including PI3K-AKT and MAPK-ERK pathways, and promoted hormone-independent growth in MCF7 and T47D cells. Enforced expression of the LMNA-NTRK1 fusion conferred resistance to the ER antagonist fulvestrant and combined treatment of fulvestrant and the Trk inhibitor larotrectinib completely blocked the growth of LMNA-NTRK+ breast cancer cells. Similarly, expression of the EML4-ALK fusion also activated growth factor signaling pathways and caused resistance to estrogen depletion and induced sensitivity to the ALK inhibitor, Ceritinib. Treatment of xenografted LMNA-NTRK1 expressing tumors confirmed the efficacy of the combined treatment of antiestrogen and NTRK1 inhibition in vivo. Two patients with acquired LMNA-NTRK1 fusions and metastatic disease received larotrectinib and demonstrated clinical benefit. Overall, our findings demonstrate that kinase fusions promote endocrine resistance in ER-positive breast cancer, and suggest that fusion screening in advanced breast cancer, particularly those with ER-positive breast cancer at progression on hormone therapy can identify rare tumors harboring targetable kinase fusions.

Citation Format: Bo Liu, Dara S. Ross, Alison M. Schram, Pedram Razavi, Stephen M. Lagana, Yanming Zhang, Maurizio Scaltriti, Jacqueline F. Bromberg, Marc Ladanyi, David M. Hyman, Alexander Drilon, Ahmet Zahir, Ryma Benayed, Jaclyn F. Hechtman, Sarat Chandarlapaty. Kinase fusions drive endocrine resistance in estrogen receptor-positive breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5280.

Abstract 5680: TRK xDFG mutations trigger a sensitivity switch from type I to II kinase inhibitors

Background: TRK inhibition is the standard of care for patients with TRK fusion-positive solid tumors. TRK kinase domain mutations that impair drug binding are common mechanisms of resistance to 1st-generation TRK inhibitors. While 2nd-generation TRK inhibitors were designed to maintain kinase inhibition in this setting, the resistance to these agents is still poorly characterized.

Methods and Results: We sequenced paired tumor biopsies and serial cell-free DNA (cfDNA) collected before therapy and at progression from patients treated with 2nd-generation TRK inhibitors (selitrectinib or repotrectinib). We identified 5 cases in which the acquisition of xDFG (G667) TRKA mutations was associated with resistance. Two patients whose tumors carried these substitutions pre-selitrectinib never responded to therapy, while three additional cases acquired these mutations upon progression to either selitrectinib or repotrectinib.

In-silico molecular modeling combined with molecular dynamic simulations predicted that TRKA xDFG substitutions can confer resistance to 2nd-generation TRK inhibitors by generating steric hindrance that compromises drug binding. Accordingly, in vitro kinase assays showed that the IC50 for selitrectinib of TRKA xDFG mutants was &gt;12 to &gt;8000 fold higher compared to the IC50 of either TRKA wild type or the selitrectinib-sensitive TRKA G595R solvent front mutant.

Interestingly, our data also suggest that TRKA xDFG substitutions induce conformational changes that stabilize the inactive (xDFG-out) conformation of the kinase, thus sensitizing it to type II inhibition. In vitro microscale thermophoresis revealed that the binding affinity of type II TRK inhibitors (cabozantinib or foretinib) to the TRKA G667C-mutant kinase was 8-10-fold higher compared to the type I inhibitor selitrectinib. We then tested the efficacy of type II TRK inhibitors against TRKA xDFG mutants in different cell models. A Bcan-Ntrk1-driven mouse model knocked in by CRISPR Cas9 to express the xDFG mutations was sensitive to type II but not to type I TRK inhibitors. Similar results were obtained using an LMNA-NTRK1-positive colorectal cell line that acquired the G667C substitution upon chronic selitrectinib treatment.

Type II TRK inhibitor therapy achieved complete and durable responses also in patient-derived models with TRKA xDFG-mediated resistance to type I 2nd-generation agents.

Conclusions: Our study uncovers a molecular switch induced by xDFG mutations that limits the sensitivity to type I kinase inhibitors by conformational changes that favor the inactive xDFG-out kinase state. This same switch in turn sensitizes these mutant kinases to type II inhibitors that effectively engage this inactive conformation. These results provide a paradigm for the rational development of 3rd-generation TKIs that address the problem of conformational resistance in tumors that are driven by oncogenic kinases.

Citation Format: Emiliano Cocco, Ji Eun Lee, Srinivasaraghavan Kannan, Alison M. Schram, Helen H. Won, Sophie Shifman, Amanda Kulick, Laura Baldino, Eneda Toska, Sabrina Arena, Benedetta Mussolin, Ram Kannan, Neil Vasan, Alexander N. Gorelick, Michael F. Berger, Yi Liao, Uwe Rix, Alberto Bardelli, Jacklyn Hechtman, Elisa de Stanchina, David M. Hyman, Chandra Verma, Andrea Ventura, Alexander Drilon, Maurizio Scaltriti. TRK xDFG mutations trigger a sensitivity switch from type I to II kinase inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5680.

Discovery through clinical sequencing in oncology

The molecular characterization of tumors now informs clinical cancer care for many patients. This advent of molecular oncology is driven by the expanding number of therapeutic biomarkers that can predict sensitivity to both approved and investigational agents. Beyond its role in driving clinical trial enrollments and guiding therapy in individual patients, large-scale clinical genomics in oncology also represents a rapidly expanding research resource for translational scientific discovery. Here, we review the progress, opportunities, and challenges of scientific and translational discovery from prospective clinical genomic screening programs now routinely conducted in cancer patients.

Abstract 16: Landscape and outcome of TRK fusion-positive Cancers

TRK inhibitors achieve marked tumor-agnostic efficacy in TRK fusion-positive cancers and consequently are now an established standard of care. Little is known, however, about the demographics, clinical outcomes, response to alternative standard therapies, or genomic characteristics of TRK fusion-positive cancers. Utilizing a center-wide screening program involving more than 26,000 prospectively sequenced patients, genomic and clinical data from all cases with identified TRK fusions were extracted. An integrated analysis was performed of genomic, therapeutic, and phenomic outcomes. In total, we identified 76 cases with confirmed TRK fusions (0.27% overall prevalence) involving 48 unique rearrangements and 17 distinct cancer types. The presence of a TRK fusion was associated with depletion of concurrent oncogenic drivers (p=4.4E-7) and lower tumor mutation burden (p=4.2E-9), with the exception of colorectal cancer where TRK fusions co-occur with microsatellite instability (MSI-H). Longitudinal profiling in a subset of patients indicated that TRK fusions were present in all sampled timepoints in 82% (14/17) of cases. Progression-free survival on first-line therapy, excluding TRK inhibitors, administered for advanced disease was 9.6 months (95% CI: 4.8-13.2). The best ORR achieved with chemotherapy containing-regimens across all lines of therapy was 63% (95% CI: 41-81). Among 12 patients treated with checkpoint inhibitors, the only response observed was in an MSI-H colorectal patient. TRK fusion-positive cancers can respond to alternative standards of care, although efficacy of immunotherapy in the absence of other predictive biomarkers (MSI-H) appears limited. TRK fusions are present in tumors with simple genomes lacking in concurrent drivers that may partially explain the tumor-agnostic efficacy of TRK inhibitors.

Citation Format: Ezra Y. Rosen, Debra A. Goldman, Jaclyn F. Hechtman, Ryma Benayed, Alison M. Schram, Emiliano Cocco, Sophie Shifman, Yixiao Gong, Ritika Kundra, James P. Solomon, Alberto Bardelli, Maurizio Scaltriti, Alexander Drilon, Alexia Iasonos, Barry S. Taylor, David M. Hyman. Landscape and outcome of TRK fusion-positive Cancers [abstract]. In: Proceedings of the AACR Special Conference on Advancing Precision Medicine Drug Development: Incorporation of Real-World Data and Other Novel Strategies; Jan 9-12, 2020; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_1):Abstract nr 16.

Masterkey-01: Phase I/II, open-label multicenter study to assess safety, tolerability, pharmacokinetics, and antitumor activity of BDTX-189, an inhibitor of allosteric ErbB mutations, in patients with advanced solid malignancies

TPS3665

Background: A significant unmet need exists for drugs targeting allosteric ErbB mutations (non-canonical mutations outside the ATP binding site). Current EGFR and HER2 tyrosine kinase inhibitors or mAbs have limited antitumor activity against allosteric mutations, resulting in toxicity before adequate drug exposure (Connell and Doherty, 2017). BDTX-189 is a potent and selective orally available irreversible inhibitor targeting unique oncogenic driver mutations of ErbB kinases in EGFR and HER2, while sparing WT EGFR. Preclinical studies demonstrated antitumor activity across a range of allosteric ErbB mutants, including extracellular domain allosteric mutations of HER2 as well as EGFR and HER2 kinase domain exon 20 insertions (Buck, 2019). This first-in-human trial (NCT04209465) is aimed to determine the recommended phase 2 dose (RP2) and schedule (Phase 1, P1), and evaluate the efficacy (Phase 2, P2) of BDTX-189. P1 primary objective is to determine the RP2 dose and schedule of monotherapy BDTX-189. Secondary objectives include assessment of safety, tolerability, pharmacokinetics (PK), pharmacodynamic (PD) effects in tumor, and preliminary efficacy. The P2 primary objective is to assess antitumor activity of monotherapy BDTX-189. Methods: The study will enroll patients (pts) ≥18 yrs with histologically or cytologically confirmed locally advanced or metastatic solid tumors with no standard therapy available or for whom standard therapy is unsuitable or intolerable. P1 dose-escalation will use a BOIN design (Yuan, 2016) and will enroll ≤ 88 pts with allosteric HER2 or HER3 mutation; EGFR or HER2 exon 20 insertion mutation; HER2 amplified or overexpressing tumor; or EGFR exon 19 deletion or L858R mutation. BDTX-189 will be dosed orally (PO) initially QD in 3 wk cycles. Regimen optimization will use PK, PD and safety data and may explore a BID schedule. An expansion cohort of ≤12 pts will further evaluate safety and preliminary efficacy of BDTX-189 prior to P2. P2, utilizing a Simon 2-stage design, will enroll ≤100 pts with NSCLC with EGFR or HER2 exon 20 insertion mutations (cohort 1); breast cancer with an allosteric ErbB mutation (cohort 2); tumors (except breast) with S310F/Y mutation (cohort 3); and other allosteric ErbB mutations not defined in cohorts 1-3 (cohort 4). Assessments include safety, tolerability, DLTs, evaluation of MTD, PK, PD, and preliminary antitumor activity. Enrollment began 1/2020. Clinical trial information: NCT04209465 .

The impact of poly ADP ribose polymerase (PARP) inhibitors on clonal hematopoiesis

1513

Background: Poly (ADP-ribose) polymerase (PARP) inhibitors are an important new class of anti-cancer therapies. Therapy-related myeloid neoplasia (tMN) has been reported following PARPi therapy, and is associated with adverse outcomes. Further insight is required into the risk of tMN conferred by PARPi therapy, independent of germline genetic background and prior therapy. We have shown that oncologic therapy selects for acquired mutations in the blood (clonal hematopoiesis; CH) particularly those in the DNA damage response pathway (DDR) including PPM1D, TP53 and CHEK2 and that CH confers an increased risk of tMN. We hypothesized that characterization of the relationship between CH and PARPi therapy provides insight into its potential for leukemogenesis and may offer opportunities for tMN prevention. Methods: We assessed for CH in the blood of 10,156 cancer patients, including 54 who received PARPi therapy, 5942 who received another systematic therapy or radiation therapy and 4160 untreated prior to blood draw. Results: Patients exposed to PARPi therapy were more likely to have CH (33%) compared to those exposed to other systemic therapies or radiation (18%) or untreated patients (16%). This was particularly pronounced for DDR CH; 25% of PARPi treated patients had DDR CH compared to 2% of untreated patients. In a multivariable model accounting for demographics, exposure to chemotherapeutic agents, radiation therapy and germline BRCA mutation status, exposure to PARPi conferred an increased risk of DDR CH (OR = 3.6, 95% CI 1.5-8.5, p = 0.004). This effect was attenuated after accounting for cumulative exposure to therapy (OR = 2.8, 95% CI 0.97-8.2, p = 0.06) suggesting a multifactorial contribution to the enrichment of CH following PARPi therapy. To characterize this further we performed a prospective collection of patients with CH over a median follow-up time of 58 months. During the follow-up period, 17 patients received PARPi, 360 received cytotoxic therapies or radiation and 232 were untreated or received targeted therapies. The growth rate of DDR CH was significantly higher among those who were exposed to PARPi (median, +2.8% increase in VAF per year) compared to untreated patients (+0.08% per year, p = 0.02) and those exposed to other cytotoxic therapies (+1% per year, p = 0.04). Conclusions: Taken together our data suggests that PARPi therapy promotes the expansion of DDR CH. Future studies should examine the potential of CH to identify individuals at high risk of tMN following PARPi therapy and to develop therapies aimed to prevent tMN in patients with CH.

Basket study of the oral progesterone antagonist onapristone ER in women with progesterone receptor positive (PR+) recurrent granulosa cell tumor (GCT), low-grade serous ovarian cancer (LGSOC), or endometrioid endometrial cancer (EEC)

TPS6098

Background: Onapristone extended release (ER) is a type I full progesterone antagonist that inhibits progesterone mediated PR activation and stabilizes PR association with corepressors. Onapristone has shown activity across multiple preclinical models of hormonally driven cancer. A phase I dose escalation study of onapristone ER in PR+ breast, endometrial and ovarian cancer patients found all doses tested to be well tolerated, with 50mg PO BID determined to be the recommended phase 2 dose (RP2D). GCT (98% of cases PR+), LGSOC (58% of cases PR+) and EEC (67% of cases PR+) are hormonally driven cancers which generally have poor responses to chemotherapy and limited treatment options in the recurrent setting. Methods: This is an open-label, investigator-initiated basket study of onapristone ER in patients with PR+ recurrent GCT, LGSOC, or EEC currently enrolling patients at Memorial Sloan Kettering Cancer Center in NY, USA (NCT03909152). The primary objective is to evaluate the efficacy, in terms of response rate by RECIST 1.1 criteria, within 36 weeks of treatment. Eligible patients must have received at least 1 prior line of chemotherapy, have measurable disease by RECIST 1.1 criteria, and have tumor tissue collected within 3 years prior to enrollment with PR expression ≥ 1% by IHC. Patients are allowed to have unlimited additional prior lines of chemotherapy, biologic therapy, immunotherapy or hormonal therapy. Enrolled patients are treated with onapristone ER 50mg PO BID until time of progression or intolerable toxicity. The 3 disease cohorts are currently enrolling to Stage I in parallel with expansion from stage I to stage II planned when the prespecified response criteria are met for each cohort as described in the table below. Clinical trial information: NCT03909152. [Table: see text]

Results of a first-in-human phase I study of SRF231, a fully human, high-affinity anti-CD47 antibody

3064

Background: CD47 is a transmembrane protein that acts as a “Don’t Eat Me” signal to evade immune recognition. It is overexpressed in multiple cancer subtypes and is associated with poor prognosis. SRF231 is an investigational, fully human, high-affinity CD47-targeting antibody that delivers an activating signal to myeloid cells and displays favorable preclinical characteristics regarding its receptor occupancy/tumor exposure/efficacy relationship. Methods: In a Phase 1 study, SRF231-101 (NCT03512340), patients with advanced solid and hematologic malignancies who had failed standard therapy were enrolled in dose escalation cohorts (accelerated single-patient followed by standard 3+3) to establish the preliminary safety of SRF231 as a monotherapy and identify a dose and schedule suitable for expansion. In addition to collection of safety data, clinical outcomes were evaluated based on Response Evaluation Criteria in Solid Tumors (RECIST v1.1) and SRF231 pharmacokinetic (PK) and pharmacodynamic (receptor occupancy) analyses were performed. Results: As of January 11, 2020, a total of 46 patients were enrolled, 25 in every-3-week intravenous (IV) dosing schedules and 21 in weekly IV dosing schedules. Weekly dosing schedules also explored the use of a 1.0 mg/kg initiation dose. Other than one patient with recurrent follicular lymphoma, all patients had recurrent/refractory solid tumors. The most common treatment emergent adverse events across dosing schedules were low-grade fatigue (43%), headache (35%), and pyrexia (30%). On every-3-week dosing schedules, 2 dose-limiting toxicities (DLTs) were observed: Grade 3 febrile neutropenia and Grade 3 hemolysis, both at a 12.0 mg/kg dose level. On weekly dosing schedules, 3 DLTs were observed: Grade 4 thrombocytopenia (6.0 mg/kg), Grade 4 amylase and lipase increased (4.0 mg/kg with initiation dose), and Grade 3 fatigue (4.0 mg/kg). The maximum tolerated dose was 9.0 mg/kg on an every-3-week and 4.0 mg/kg on a weekly schedule. Receptor occupancy was maintained at > 90% throughout the dosing period with a 4.0 mg/kg weekly dose schedule. Out of 37 patients who were response evaluable by RECIST, there were no complete or partial responders, although prolonged stable disease has been observed. Conclusions: Preliminary data from a Phase 1 study of SRF231, an anti-CD47 antibody, demonstrate that SRF231 may be administered safely and doses of 4.0 mg/kg weekly maintain > 90% receptor occupancy throughout the dosing period. Updated safety data, clinical outcomes, and PK/pharmacodynamic data will be presented. Clinical trial information: NCT03512340 .