Characterization and management of ERK inhibitor associated dermatologic adverse events: analysis from a nonrandomized trial of ulixertinib for advanced cancers

Background Ulixertinib is the first-in-class ERK1/2 kinase inhibitor with encouraging clinical activity in BRAF- and NRAS-mutant cancers. Dermatologic adverse events (dAEs) are common with ulixertinib, so management guidelines like those established for epidermal growth factor receptor inhibitor (EGFRi)-associated dAEs are needed. Patients and Methods This was an open-label, multicenter, phase I dose escalation and expansion trial of ulixertinib evaluating data from 135 patients with advanced malignancies enrolled between March 2013 and July 2017. Histopathological features, management, and dAEs in 34 patients are also reported. Twice daily oral ulixertinib was administered at 10 to 900 mg in the dose escalation cohort (n = 27) and at 600 mg in 21-day cycles in the expansion cohort (n = 108). Results The incidence of ulixertinib-induced dAEs and combined rash were 79% (107/135) and 76% (102/135). The most common dAEs included acneiform rash (45/135, 33%), maculopapular rash (36/135, 27%), and pruritus (34/135, 25%). Grade 3 dAEs were observed in 19% (25/135) of patients; no grade 4 or 5 dAEs were seen. The presence of at least 1 dAE was associated with stable disease (SD) or partial response (PR) (OR = 3.64, 95% CI 1.52-8.72; P = .003). Acneiform rash was associated with a PR (OR = 10.19, 95% CI 2.67-38.91; P < .001). Conclusion The clinical spectrum of ulixertinib-induced dAEs was similar to EGFR and MEK inhibitors; dAEs may serve as a surrogate marker of tumor response. We propose treatment algorithms for common ERK inhibitor-induced dAEs to maintain patients' quality of life and dose intensity for maximal clinical benefit. Clinical Trial Registration: NCT01781429.

Characterization of on-target adverse events caused by TRK inhibitor therapy

BACKGROUND

The tropomyosin receptor kinase (TRK) pathway controls appetite, balance, and pain sensitivity. While these functions are reflected in the on-target adverse events (AEs) observed with TRK inhibition, these AEs remain under-recognized, and pain upon drug withdrawal has not previously been reported. As TRK inhibitors are approved by multiple regulatory agencies for TRK or ROS1 fusion-positive cancers, characterizing these AEs and corresponding management strategies is crucial.

PATIENTS AND METHODS

Patients with advanced or unresectable solid tumors treated with a TRK inhibitor were retrospectively identified in a search of clinical databases. Among these patients, the frequency, severity, duration, and management outcomes of AEs including weight gain, dizziness or ataxia, and withdrawal pain were characterized.

RESULTS

Ninety-six patients with 15 unique cancer histologies treated with a TRK inhibitor were identified. Weight gain was observed in 53% [95% confidence interval (CI), 43%-62%] of patients and increased with time on TRK inhibition. Pharmacologic intervention, most commonly with glucagon-like peptide 1 analogs or metformin, appeared to result in stabilization or loss of weight. Dizziness, with or without ataxia, was observed in 41% (95% CI, 31%-51%) of patients with a median time to onset of 2 weeks (range, 3 days to 16 months). TRK inhibitor dose reduction was the most effective intervention for dizziness. Pain upon temporary or permanent TRK inhibitor discontinuation was observed in 35% (95% CI, 24%-46%) of patients; this was more common with longer TRK inhibitor use. TRK inhibitor reinitiation was the most effective intervention for withdrawal pain.

CONCLUSIONS

TRK inhibition-related AEs including weight gain, dizziness, and withdrawal pain occur in a substantial proportion of patients receiving TRK inhibitors. This safety profile is unique relative to other anticancer therapies and warrants careful monitoring. These on-target toxicities are manageable with pharmacologic intervention and dose modification.

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.

Final results from the phase I study expansion cohort of the selective FGFR inhibitor Debio 1,347 in patients with solid tumors harboring an FGFR gene fusion

3603

Background: Debio 1347 is a selective oral inhibitor of FGFR 1-3 tyrosine kinases. It exhibited high antitumor activity in in vitro and in vivo tumor models with FGFR1-3 gene fusions. Here we report the results of the expansion portion of a Phase 1 study of advanced solid tumors patients (pts) harboring an FGFR1-3 gene fusion. Methods: Pts with advanced refractory solid tumors harboring an FGFR1-3 gene fusion were enrolled. Based on results from the dose escalation portion, pts received Debio1347 80 mg once daily (qd) in 28-day cycles. Pharmacokinetics (PK) and pharmacodynamics were evaluated. The data cut-off was October 8, 2019. Results: Among 18 pts enrolled, 5 had primary brain tumors (PBT), 5 had cholangiocarcinoma, 2 had urothelial cancer, 2 had colon cancer, 1 patient each lung neoplasm, gastric cancer, endometrial cancer and squamous cell carcinoma of the chest wall. Tumors harbored fusions with FGFR1 (n = 1), FGFR2 (n = 8), and FGFR3 (n = 9). All had prior systemic therapy (median 3 lines; range 1-4). The most common treatment emergent adverse events were fatigue (50%), hyperphosphatemia (44.4%), anemia (38.9%), alopecia (33.3%), nausea (33.3%), vomiting (33.3%), constipation (33.3%), and palmar-plantar erythrodysesthesia syndrome (22.2%). Blurred vision was reported in 1 pt. There were no findings on ocular exams compatible with retinal detachment. No grade 3 AE related to study drug were reported. One patient needed dose reduction due to grade 2 nails toxicity. In PK analysis, plasma steady-state was rapidly achieved and serum phosphate increase correlated with Debio 1347 plasma exposure, confirming target engagement at 80 mg qd. Median follow-up was 18 weeks. Partial responses were observed in 3 pts harboring an FGFR2 fusion: 1 out of 2 colon cancer and 2 out 5 cholangiocarcinoma. Median duration of response was 16.1 weeks (range: 8.4-22.8+). Overall disease control was observed in 11 out of 14 pts without PBT (79%). Median PFS was 18.3 weeks. No signs of activity were observed in the 5 patients with PBT, all with an FGFR3-TACC3 fusion. Conclusions: Debio 1347 at the recommended dose of 80 mg qd was generally well tolerated and showed signs of activity in solid tumors harboring an FGFR fusion. The FUZE phase 2 clinical trial of Debio 1347 is recruiting FGFR fusion-positive advanced solid tumors irrespectively of tumor histology, excluding PBT. Clinical trial information: NCT01948297 .

Enrichment of kinase fusions in ESR1 wild-type, metastatic breast cancer revealed by a systematic analysis of 4854 patients

BACKGROUND

Kinase fusions are rare and poorly characterized in breast cancer (BC). We aimed to characterize kinase fusions within a large cohort of advanced BC.

PATIENTS AND METHODS

A total of 4854 patients with BC were analyzed by Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) targeted DNAseq and MSK-Fusion targeted RNAseq during the study time period.

RESULTS

Twenty-seven of 4854 (0.6%) patients harbored fusions: 11 FGFR (five FGFR2, three FGFR3, three FGFR1), five BRAF, four NTRK1, two RET, two ROS1, one ALK, one ERBB2, and one MET. A history of endocrine therapy was present in 15 (56%) of fusion-positive BC; eight of the 15 cases had available pre-treatment samples, of which six were fusion-negative. None of the fusion-positive BC samples harbored ESR1 hotspot mutations. Two patients with acquired LMNA-NTRK1 fusions and metastatic disease received larotrectinib and demonstrated clinical benefit.

CONCLUSION

Kinase fusions in BC are extremely rare, and appear to be enriched in hormone-resistant, metastatic carcinomas and mutually exclusive with ESR1 mutations. The present study expands the spectrum of genetic alterations activating mitogen-activated protein kinase (MAPK) signaling that can substitute for ESR1 mutations in this setting. Molecular testing at progression after endocrine therapy should include fusion testing, particularly in the absence of ESR1 hotspot alterations, in an effort to identify additional therapeutic options which may provide substantial clinical benefit.

Genomic alterations in breast cancer: level of evidence for actionability according to ESMO Scale for Clinical Actionability of molecular Targets (ESCAT)

Better knowledge of the tumor genomic landscapes has helped to develop more effective targeted drugs. However, there is no tool to interpret targetability of genomic alterations assessed by next-generation sequencing in the context of clinical practice. Our aim is to rank the level of evidence of individual recurrent genomic alterations observed in breast cancer based on the ESMO Scale for Clinical Actionability of molecular Targets (ESCAT) in order to help the clinicians to prioritize treatment. Analyses of databases suggested that there are around 40 recurrent driver alterations in breast cancer. ERBB2 amplification, germline BRCA1/2 mutations, PIK3CA mutations were classified tier of evidence IA based on large randomized trials showing antitumor activity of targeted therapies in patients presenting the alterations. NTRK fusions and microsatellite instability (MSI) were ranked IC. ESR1 mutations and PTEN loss were ranked tier IIA, and ERBB2 mutations and AKT1 mutations tier IIB. Somatic BRCA 1/2 mutations, MDM2 amplifications and ERBB 3 mutations were ranked tier III. Seventeen genes were ranked tier IV based on preclinical evidence. Finally, FGFR1 and CCND1 were ranked tier X alterations because previous studies have shown lack of actionability.

Efficacy and safety of larotrectinib in patients with TRK fusion gastrointestinal cancer

824

Background: Tropomyosin receptor kinase (TRK) fusions arise from rearrangements of the neurotrophic tyrosine receptor kinase ( NTRK) 1, 2, or 3 genes and an unrelated gene, creating constitutively active oncogenic drivers that have been detected in a range of adult and pediatric malignancies, but are generally rare in patients with gastrointestinal (GI) cancer. Larotrectinib is a selective TRK inhibitor approved for the treatment of adult and pediatric patients with TRK fusion cancer. Here, we report efficacy and safety data for patients with TRK fusion GI tumors. Methods: Patients with a TRK fusion GI cancer treated with larotrectinib in a phase II clinical trial, NAVIGATE (NCT02576431), were included in this analysis. Larotrectinib was administered at 100 mg twice daily, until disease progression, unacceptable toxicity, death, or withdrawal. Response was assessed by the investigator using RECIST v1.1. Results: As of February 19, 2019, 14 patients with TRK fusion GI cancer (median age 68 y, range 32–84 y) were enrolled. GI tumor types were colon (8), cholangiocarcinoma (2), pancreas (2), appendix (1), and hepatic (1). Fusions involved NTRK1 (n = 12) and NTRK3 (n = 2). Nine patients had ≥2 prior lines of therapy. The best response on last prior therapy was 1 partial response (PR). Overall best responses on larotrectinib were: colon cancer, 4 patients had a PR and 4 had stable disease (SD); pancreatic cancer, 1 patient had a PR and 1 had SD; cholangiocarcinoma, 1 patient had a PR and 1 had progressive disease; appendix cancer, 1 patient had SD; response in 1 patient with hepatic cancer was not determined. Median time to response was 1.8 months (range 1.7–2.1). With 5 patients ongoing and censored, the median progression free survival was 5.3 months (95% CI 2.2–9.0). Median overall survival was 33.4 months (95% CI 2.8–36.5). Larotrectinib was well tolerated, with most adverse events being grade 1 or 2. Conclusions: Although the sample size is limited, there is evidence of clinical activity with larotrectinib in TRK fusion GI cancer, with a manageable safety profile. TRK fusion GI cancer may represent an under-diagnosed subset of patients with viable treatment options. Clinical trial information: NCT02576431.

FUZE clinical trial: a phase 2 study of Debio 1347 in FGFR fusion-positive advanced solid tumors irrespectively of tumor histology

TPS3157

Background: Dysregulation of fibroblast growth factor receptor (FGFR) signaling by FGFR fusions is implicated in many cancers. Debio 1347 is a selective oral inhibitor of FGFR 1-3 tyrosine kinases. It exhibited high antitumor activity in in vitro and in vivo tumor models with FGFR1-3 gene fusions. Preliminary data from an ongoing phase 1 trial show efficacy and tolerability in patients (pts) harboring FGFR 1-3 fusion irrespectively of tumor type. We present the design for a multicenter, basket, 2-stage, adaptive single arm Phase 2 trial investigating Debio 1347 in pts with solid tumors harboring FGFR1-3 fusion/rearrangement. Methods: Adults with locally advanced/unresectable or metastatic tumors with documented FGFR1-3 gene fusion/rearrangement who require systemic therapy and have progression after ≥1 prior standard treatment or have no satisfactory alternative treatment option are eligible. Three cohorts are included: biliary tract cancer (cohort 1), urothelial cancer (cohort 2) and all other solid tumors (cohort 3). Primary brain tumors are excluded. Other key exclusion criteria include prior treatment with FGFR1-3 selective inhibitor; clinically significant corneal/retinal disorder; history of calcium/phosphate homeostasis disorder or systemic mineral imbalance with ectopic soft tissue calcification, and symptomatic/unstable brain metastases < 1 month before enrollment. Genomic screening of tumor tissue is done at local or central laboratory with post-hoc central confirmation by RNA sequencing. Eligible pts will receive Debio 1347, 80 mg PO once daily in 28-day cycles until occurrence of progression or unacceptable toxicity. Primary Endpoint is objective response rate (ORR) based on independent central review using RECIST v.1.1. The targeted sample size (N=125) will provide approximately 90% power to reject H0: ORR ≤ 15% at an overall 5% significance level based on an expected ORR of 30% in at least one of the cohorts. Secondary endpoints are: duration of response, disease control rate, progression-free survival, overall survival, safety, tolerability, and quality of life. An interim analysis for futility and homogeneity will be performed after 27 evaluable pts. PK sparse sampling is performed to assess exposure-response relationships with efficacy and safety. Biomarkers of response and resistance will be explored. Accrual is opened in US, EU, Asia and Australia. Clinical trial information: NCT03834220.

Benefit of early-phase targeted, basket, and immune-based trials for patients with chemorefractory gastrointestinal (GI) cancers

e15700

Background: Historically, phase I trials were designed to establish phase II tolerable doses of new drugs. Efficacy concerns were secondary. In the modern era of targeted and immune-based therapies, investigator and patient expectations of efficacy in such trials have increased. Patients (pts) who have exhausted standard treatment options often seek participation in phase I drug development or phase II basket studies, with hope for therapeutic benefit. We assessed the benefit to pts with chemorefractory GI cancers from investigational early drug development trials at our institution. Methods: We reviewed the referral records of our Early Drug Development and Immunotherapy Services to identify pts referred from our GI Oncology Service in 2018. As pts are typically not referred unless with performance status 0-1, and normal liver, renal, and marrow function, those requesting early phase studies but not meeting these criteria were excluded from this analysis. End points were enrollment on a trial, 3 and 6-month PFS, and tumor shrinkage. Results: Of 245 GI Oncology pts referred in 2018, 26 (11%) were accrued to a trial: 14 to immune-based (1 withdrew before treatment) and 12 to targeted (3 to phase II basket): median age 53 (range 23-76); 15 female. GI cancer types included: colon (7), pancreas (7), cholangiocarcinoma (4), rectal (3), and appendiceal, peritoneal mesothelioma, small bowel, unknown primary, and gastric (1). Most common reasons for non-accrual were lack of available treatment spots and failure to meet eligibility criteria for specific trials. Of 22 pts with adequate follow up at time of analysis, none achieved 6-month PFS; one (5%) met 3-month PFS with tumor growth below RECIST criteria at 3 months and came off study for progression at 4 months. No pts achieved any degree of tumor shrinkage while receiving trial drugs. Conclusions: Phase I and phase II basket options for chemorefractory GI cancers were limited relative to demand. Benefit from investigational treatment in this patient population was limited; expectations may be overstated. Further research is underway to evaluate pts’ expectations for therapeutic benefit from early phase targeted and immune-based trials.

Non-invasive detection of acquired resistance to FGFR inhibition in patients with cholangiocarcinoma harboring FGFR2 alterations

4096

Background: FGFR2 alterations are present in 14% of cholangiocarcinomas (CCA) and are promising targets of investigational FGFR-directed therapies. Cell-free DNA profiling has emerged as a non-invasive approach to monitor disease and longitudinally characterize tumor evolution. We describe the use of circulating tumor DNA (ctDNA) among patients (pts) with FGFR2-altered CCA receiving FGFR-targeted therapy in the identification of acquired FGFR2 mutations (mut) at resistance. Methods: Serial blood samples were collected from 8 pts with FGFR-altered CCA for ctDNA isolation and next generation sequencing. Plasma ctDNA collected at baseline and resistance to FGFR-targeted therapy were sequenced using a custom ultra-deep coverage cfDNA panel, MSK-ACCESS, incorporating dual index primers and unique molecular barcodes to enable background error suppression and high-sensitivity mut detection. The assay was enhanced to include all protein-coding exons and relevant introns of FGFR2. In 5/8 pts, genomic profiling of an initial tumor biopsy was performed. Results: 8 pts with FGFR2-altered CCA (7 gene fusions, 1 amplification) were treated with FGFR-targeted therapies. 7/8 pts exhibited stable disease or partial response. 19 total acquired mut in FGFR2 were detected at resistance in 5/8 pts (between 1-9 unique mut identified in each sample). All mut were located in the kinase domain. Conclusions: Acquired mut in FGFR2 are seen in pts who have developed resistance to targeted therapy. CtDNA can be used to identify these mut at the time of acquired resistance. The multitude of FGFR2 mut observed within individual pts suggest heterogeneity and evolutionary convergence of resistance mechanisms. Our results illustrate the utility of ctDNA as a less invasive way to monitor for signs of resistance and to identify other potential targetable alterations. [Table: see text]

Safety and preliminary clinical activity of repotrectinib in patients with advanced ROS1 fusion-positive non-small cell lung cancer (TRIDENT-1 study)

9011

Background: Repotrectinib is a next-generation ROS1/TRK/ALK TKI inhibiting ROS1 with > 90-fold greater potency than crizotinib. Preclinical studies showed robust kinase inhibitory activity of repotrectinib against all known ROS1 fusion positive resistance mutations, including the most common ROS1 solvent-front mutation (SFM) G2032R. Methods: In this ongoing phase 1 study (NCT03093116), TKI-naïve and TKI-refractory (≥1 TKI) patients (pts) with advanced ROS1/TRK/ALK+ solid tumors received repotrectinib treatment. Endpoints include safety, PK, and confirmed overall response (cORR). Safety analysis for all pts (n = 75) and efficacy analysis for ROS1+ NSCLC pts (n = 28) enrolled on the study was conducted. Results: As of 31-Oct-2018, 75 pts were treated with repotrectinib at dose levels from 40 mg QD to 200 mg BID. Most AEs were manageable and grade (Gr) 1-2. Common ( > 20%) treatment-related AEs were dizziness (49%), dysgeusia (48%), paresthesia (28%), and constipation (20%). Four DLTs (Gr3 dyspnea/hypoxia (n = 1); Gr2 (n = 1) and Gr3 (n = 1) dizziness at 160 mg BID, and Gr3 dizziness (n = 1) at 240 mg QD) occurred and were managed with dose modifications. The MTD has not been reached. Median number of prior TKI treatment was 1 (0-3) with all of TKI naïve and 83% of TKI pre-treated pts received prior chemotherapy. Among 10 evaluable TKI-naïve ROS1+ NSCLC pts, confirmed ORR by Blinded Central Review (BCR) was 90% (95% CI 56 - 100) with median duration of response (DOR) not reached ((range 5.5+ – 14.9+ months (mos)). Among 18 TKI-pretreated pts, confirmed ORR by BCR was 28% (95% CI 10 – 54) with DOR of 10.2 mos. Subgroup analysis showed cORR 44% (95% CI 14 - 79) in 9 prior TKI pts and treated at dose levels of 160 mg QD or above. In 7 pts with measurable target CNS lesions at baseline, the intracranial ORR was 3/3 (100%) with DOR (5.5+; 7.2+; 14.85+ mo) in TKI-naïve pts and 2/4 (50%) with DOR (5.5+;14.8+, mo) in TKI-pretreated pts, respectively. Conclusions: Repotrectinib was well tolerated and demonstrated encouraging overall and intracranial clinical activity in pts with ROS1 fusion-positive NSCLC. Enrollment in phase 1 continues until the RP2D is determined. A global phase 2 study is planned. Clinical trial information: NCT03093116.

Ado-trastuzumab emtansine in patients with HER2 amplified salivary gland cancers (SGCs): Results from a phase II basket trial

6001

Background: SGCs are rare tumors with no approved therapy for metastatic disease. HER2 amplification occurs in 8% among all SGC histologies, and 25-33% of the aggressive salivary duct carcinoma (SDC) histologic subtype. We hypothesized that ado-trastuzumab emtansine, a HER2 targeted antibody drug conjugate, may be clinically active in these patients. Methods: A cohort of patients with HER2 amplified SGCs were enrolled into a multi-histology basket trial of ado-trastuzumab emtansine, treated at 3.6mg/kg IV every 3 weeks. The primary endpoint was overall response rate (ORR) by RECIST v1.1 or PERCIST. A Simon two-stage optimal design was applied with type I error rate under 2.7%, power of 89%, H0 10%, H1 40%; H0 will be rejected if 6 or more responses are observed in 24 patients. Other endpoints include duration of response (DOR), progression-free survival (PFS), and toxicity. HER2 amplification was identified by next generation sequencing (NGS), and tumors were subsequently tested by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Fluorescence lifetime imaging microscopy - Förster resonance energy transfer (FLIM-FRET) assessed the propensity for HER2-HER3 heterodimerization, which leads to receptor internalization. Results: 10 patients with HER2 amplified SGCs were treated. The median age was 65 (range 36-90 years), 90% were male. The median lines of prior systemic therapy was 2 (range 0-3). ORR was 90% (9/10, 95% CI 56-100%) including 5 complete responses after prior trastuzumab, pertuzumab and anti-androgen therapy. After a median follow up period of 12 months (range 4-20 months), median DOR (range 2-19+) and median PFS (95% CI 4–22+ months) were not reached. Toxicities included grade 1 or 2 infusion reaction, thrombocytopenia and transaminitis; there were no treatment related deaths. HER2 amplification by NGS (fold change 2.8 to 22.8) correlated with HER2/CEP17≥2 by FISH (8/8 tested) or IHC3+ (10/10 tested). FLIM-FRET tested positive in 3/3. Conclusions: Ado-trastuzumab emtansine is highly efficacious in patients with HER2 amplified SGCs as identified by NGS. This study has met its primary endpoint, and cohort expansion is warranted to confirm these results. Clinical trial information: NCT02675829.

Clinicopathologic characteristics of NRG1 fusion-positive cancers: A single-institution study

3129

Background: NRG1 rearrangements are oncogenic drivers across several tumor types. Chimeric proteins encoded by NRG1 fusions activate HER3, resulting in heterodimerization with HER2 and activation of downstream signaling. Preclinical and preliminary clinical data suggest that targeting HER3 may be an effective treatment strategy for patients with NRG1 fusion-positive tumors. We aimed to describe the clinical and genomic characteristics of patients identified at our institution with NRG1 fusions. Methods: We analyzed results from prospective targeted exome and/or RNA sequencing performed at Memorial Sloan Kettering between 2014-2018 involving > 30,000 samples. NRG1 fusion-positive tumors were identified and these cases were manually reviewed. Results: NRG1 fusions were detected in 24 patients. Cancer types included lung (N = 9), pancreas (N = 7), breast (N = 5), prostate (N = 1), gallbladder (N = 1), diffuse large B-cell lymphoma (N = 1), and cancer of unknown primary (N = 1). 6/9 lung cancers had mucinous differentiation. The majority of patients were Caucasian (N = 17), half were female (N = 12) and ages ranged from 24-82 years-old. Targeted exome sequencing identified the fusion in 10/23 cases tested, including 2 not confirmed by RNA. The remaining 14 were detected using RNA. Fusion partners included CD74 (N = 6), SLC3A2 (N = 2), SDC4 (N = 2), ATP1B1 (N = 2), FOXA1 (N = 1), SLCA4 (N = 1), ROCK1 (N = 1), TNKS (N = 1), CCND1 (N = 1), PAK1 (N = 1), STAU3 (N = 1), RAD51 (N = 1), CD44 (N = 1), NCOR1 (N = 1), RBPMS (N = 1), and WHSC1L1 (N = 1). Pancreas cancers were KRAS wild-type and lung cancers had no co-occurring alterations in ALK, ROS1, EGFR, RET, MET, RAS, or RAF. All tumors were microsatellite stable. A durable response was achieved with anti-HER3 antibody therapy (GSK2849330) in a patient with a CD74- NRG1-rearranged invasive mucinous adenocarcinoma (previously reported). Four patients treated with an irreversible small molecule HER2 inhibitor (afatinib) did not respond to treatment, suggesting direct targeting of HER3 may be superior to HER2 inhibition in patients with NRG1 fusion-positive tumors. Conclusions: NRG1 fusions occur in several tumor types and may be amenable to targeting with HER3-directed therapy.

Larotrectinib efficacy and safety in adult TRK fusion cancer patients

3122

Background: A broad range of pediatric and adult malignancies harbor TRK fusions involving the NTRK1, NTRK2, and NTRK3 genes. The highly-selective TRK inhibitor, larotrectinib, has previously shown a high overall response rate (ORR) and a favorable safety profile in patients (pts) with TRK fusion cancer. To better delineate efficacy in adults, as pediatric pts have a particularly high ORR, here we report updated efficacy and safety data from the adult subset of pts with TRK fusion cancer treated with larotrectinib. Methods: Adult pts (aged 18 or older) with TRK fusion cancer detected by local testing in 2 larotrectinib clinical trials (NCT02122913 and NCT02576431) were analyzed. Larotrectinib was administered 100 mg PO BID until disease progression, withdrawal, or unacceptable toxicity. Disease status was assessed by both investigator (INV) and independent assessment (IRC) using RECIST v1.1. Results: As of July 30, 2018, 83 adults (median age: 57 y, range 20–80 y) with TRK fusion cancer had been treated. Cancer types included salivary gland (23%) and thyroid cancer (19%), soft tissue sarcoma (14%), lung cancer (13%), colon cancer and melanoma (7% each), GIST (5%), and bone sarcoma, cholangiocarcinoma, and appendiceal, breast, and pancreas cancer (≤2% each). TRK fusions involved NTRK1 (40%), NTRK2 (2%), and NTRK3 (57%). 77% of pts had received prior systemic therapy (median lines: 2, range 0–10). In 74 pts evaluable per INV, the ORR was 76% with 9% CR, 57% confirmed PR, 9% PR pending confirmation, 12% SD, 11% PD, and 1% not determined; 9 pts were non-evaluable (NE) due to lack of post-baseline assessment. In 65 pts evaluable per IRC, the ORR was 68% with 17% CR, 51% PR, 15% SD, 12% PD, and 5% NE. With a median follow up of 17.2 and 17.5 mo per INV and IRC, respectively, the median duration of response had not been reached (ranges identical: 1.9+ to 38.7+ months). At data cutoff, 63% remained on treatment; 30% had discontinued due to disease progression. Adverse events were mostly grade 1–2. Conclusions: Larotrectinib demonstrated robust tumor-agnostic efficacy and a favorable safety profile in adult pts with TRK fusion cancer. These results support testing for TRK fusion cancer in pts with advanced solid tumors, regardless of site of primary diagnosis. Clinical trial information: NCT02122913 and NCT02576431.

JAVELIN BRCA/ATM: A phase 2 trial of avelumab (anti–PD-L1) plus talazoparib (PARP inhibitor) in patients with advanced solid tumors with a BRCA1/2 or ATM defect

TPS2660

Background: Defects in DNA damage response genes, including BRCA1/2 and ATM, confer sensitivity to PARP inhibitors. Talazoparib is a potent, oral PARP inhibitor with a dual mechanism of action (PARP enzyme inhibition and PARP trapping). Avelumab is a human anti–PD-L1 IgG1 monoclonal antibody with a wild-type Fc region that has shown clinical activity in multiple tumor types. Preclinical and early clinical data suggest that combining a PARP inhibitor with an immune checkpoint inhibitor may provide improved activity. Methods: JAVELIN BRCA/ATM (NCT03565991) is an ongoing, open-label, multicenter, phase 2 trial assessing the combination of avelumab and talazoparib. Enrollment of ≈200 patients with a histologically confirmed locally advanced or metastatic solid tumor that has progressed on > 1 line of standard-of-care treatment for locally advanced or metastatic disease and has a germline or somatic defect in BRCA1 or 2 (cohort 1) or ATM (cohort 2) genes is planned. Patients with concomitant defects in > 1 gene ( BRCA1, BRCA2, or ATM) will be enrolled in cohort 1. Exclusion criteria include prior treatment with an immune checkpoint or PARP inhibitor, prior treatment with any other anticancer or radiation therapy within 2 weeks prior to enrollment, a known history of an immune-mediated or autoimmune condition, and known symptomatic brain metastases requiring steroids. The primary endpoint is confirmed objective response by blinded independent central review according to RECIST v1.1 and according to the Prostate Cancer Working Group 3 (PCWG3) for patients with metastatic castration-resistant prostate cancer (mCRPC). Secondary endpoints include safety; investigator-assessed confirmed objective response, time to tumor response, duration of response, and progression-free survival (per RECIST v1.1 and per PCWG3 for patients with mCRPC); overall survival; pharmacokinetic parameters; and potential predictive biomarkers. The study is currently enrolling patients at centers in the United States and Europe. Clinical trial information: NCT03565991.

Abstract PD3-06: Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial

Background: HER2 mutations define a rare subset of metastatic breast cancer (MBC) with a unique mechanism of oncogenic addiction to HER2 signaling. Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, has demonstrated single-agent clinical activity in HER2-mutant MBC. In HER2-mutant, HR+ MBC, neratinib + fulvestrant (N+F) appears synergistic vs single-agent neratinib, possibly due to more complete inhibition of bi-directional signaling between HER2 and estrogen receptors. Here we describe interim efficacy results of the expanded HER2-mutant, HR+ MBC cohort treated with N+F from SUMMIT (NCT01953926).

Methods: HR+ MBC patients (pts) with HER2 mutations documented by local testing received oral neratinib 240mg qd and intramuscular fulvestrant (labeled dose). Intensive loperamide prophylaxis was mandatory during cycle 1. Efficacy endpoints include objective response rate at week 8 (ORR8); confirmed objective response rate (ORR); clinical benefit rate (CBR); duration of response (DOR); progression-free survival (PFS); response was assessed by RECIST 1.1 and/or PET Response Criteria. Genomic profiling from fresh/archival tumor tissues and/or plasma cfDNA was performed retrospectively by next-generation sequencing (MSK-IMPACT).

Results: As of 18 May 2018, 46 HER2-mutant HR+ MBC pts have been treated with N+F. Most pts were pretreated, with 91% having received prior anti-cancer medication for MBC (range 0–10). ORR was 33% and median DOR in the 15 pts with a confirmed response was 9.2 months (95% CI 3.9–18.5). Twenty-four pts had prior fulvestrant exposure, and 19 had received prior CDK4/6i-based therapy. Clinical activity was observed with ORRs of 17% and 26% in prior fulvestrant-treated and prior CDK4/6i-treated pts, respectively. ORRs by HER2 mutation were: V777L 63% (5/8 pts); S310F/Y 67% (4/6 pts); G778_P780dup 50% (3/6 pts). Diarrhea was the most common adverse event (grade 3, 24%; grade 4, 0%). Median cumulative duration of grade 3 diarrhea was 3 days. There were no treatment discontinuations due to diarrhea.

 Neratinib + fulvestrantOutcomeaAll patients (N=46)Prior fulvestrant (N=24)Prior CDK4/6i-based therapy (N=19)ORR8 – n (%)19 (41.3)8 (33.3)7 (36.8)95% CI27.0–56.815.6–55.316.3–61.6ORR – n (%)15 (32.6)4 (16.7)5 (26.3)95% CI19.5–48.04.7–37.49.1–51.2DOR for each responder, months 5.6b; 9.2; 9.6b; 18.55.6b; 5.7b; 9.3; 9.6b; 12.9bCBR – n (%)27 (58.7)11 (45.8)9 (47.4)95% CI43.2–73.025.6–67.224.4–71.1Median (95% CI) time to event,c monthsPFS3.9 (3.6–5.7)3.7 (3.5–12.8)3.9 (1.9–NA)DOR9.2 (3.9–18.5)NANAaFor pts with both RECIST- and PET-evaluable lesions, the best of either RECIST or PET response was used to determine response; the earliest progression by RECIST or PET was used for progression; bPt has not progressed; cKaplan-Meier analysis; NA, not applicable

Conclusions: N+F demonstrates encouraging clinical activity with durable responses in heavily pretreated pts with HER2-mutant, HR+ MBC. Of note, responses were observed in pts who had received prior fulvestrant or CDK4/6 inhibitors. No new safety signals were identified; the rate of diarrhea was similar to single-agent neratinib and not dose limiting. Updated data after additional follow-up and genomic data will be presented.

Citation Format: Smyth LM, Piha-Paul SA, Saura C, Loi S, Lu J, Shapiro GI, Juric D, Mayer IA, Arteaga C, de la Fuente M, Brufksy AM, Mau-Sørensen M, Arnedos M, Moreno V, Sohn J-H, Schwartzberg L, Gonzàlez-Farré X, Cervantes A, Mann G, Shahin S, Cutler, Jr. RE, Eli LD, Xu F, Bagulho T, Lalani AS, Bryce R, Solit DB, Hyman DM, Meric-Bernstam F, Baselga J. Neratinib + fulvestrant for HER2-mutant, HR-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT trial [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD3-06.

Commentary on "DNA damage response and repair gene alterations are associated with improved survival in patients with platinum-treated advanced urothelial carcinoma."

PURPOSE

Platinum-based chemotherapy remains the standard treatment for advanced urothelial carcinoma by inducing DNA damage. We hypothesize that somatic alterations in DNA damage response and repair (DDR) genes are associated with improved sensitivity to platinum-based chemotherapy.

EXPERIMENTAL DESIGN

Patients with diagnosis of locally advanced and metastatic urothelial carcinoma treated with platinum-based chemotherapy who had exon sequencing with the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) assay were identified. Patients were dichotomized based on the presence/absence of alterations in a panel of 34 DDR genes. DDR alteration status was correlated with clinical outcomes and disease features.

RESULTS

One hundred patients were identified, of which 47 harbored alterations in DDR genes. Patients with DDR alterations had improved progression-free survival (9.3 vs. 6.0 months, log-rank P = 0.007) and overall survival (23.7 vs. 13.0 months, log-rank P = 0.006). DDR alterations were also associated with higher number mutations and copy-number alterations. A trend toward positive correlation between DDR status and nodal metastases and inverse correlation with visceral metastases were observed. Different DDR pathways also suggested variable effect on clinical outcomes.

CONCLUSIONS

Somatic DDR alteration is associated with improved clinical outcomes in platinum-treated patients with advanced urothelial carcinoma. Once validated, it can improve patient selection for clinical practice and future study enrollment.

Clinical and molecular characterization of patients with cancer of unknown primary in the modern era

Background

On the basis of historical data, patients with cancer of unknown primary (CUP) are generally assumed to have a dismal prognosis with overall survival of less than 1 year. Treatment is typically cytotoxic chemotherapy guided by histologic features and the pattern of metastatic spread. The purpose of this study was to provide a clinical and pathologic description of patients with CUP in the modern era, to define the frequency of clinically actionable molecular alterations in this population, to determine how molecular testing can alter therapeutic decisions, and to investigate novel uses of next-generation sequencing in the evaluation and treatment of patients with CUP.

Patients and methods

Under Institutional Review Board approval, we identified all CUP patients evaluated at our institution over a recent 2-year period. We documented demographic information, clinical outcomes, pathologic evaluations, next-generation sequencing of available tumor tissue, use of targeted therapies, and clinical trial enrollment.

Results

We identified 333 patients with a diagnosis of CUP evaluated at our institution from 1 January 2014 through 30 June 2016. Of these patients, 150 had targeted next-generation sequencing carried out on available tissue. Median overall survival in this cohort was 13 months. Forty-five of 150 (30%) patients had potentially targetable genomic alterations identified by tumor molecular profiling, and 15 of 150 (10%) received targeted therapies. Dominant mutation signatures were identified in 21 of 150 (14%), largely implicating exogenous mutagen exposures such as ultraviolet radiation and tobacco.

Conclusions

Patients with CUP represent a heterogeneous population, harboring a variety of potentially targetable alterations. Next-generation sequencing may provide an opportunity for CUP patients to benefit from novel personalized therapies.

Abstract P5-21-32: AZD5363 in combination with fulvestrant in AKT1-mutant ER-positive metastatic breast cancer

Background: E17K is the most common activating AKT1 mutation and was shown to be a therapeutic target in this multipart Phase 1 study of AZD5363 (NCT01226316), an oral and selective pan-AKT kinase inhibitor, in patients (pts) with AKT1-mutant (AKT1m) advanced solid tumors. In heavily pretreated AKT1m (E17K) ER+ metastatic breast cancer (MBC) pts, monotherapy achieved an objective response rate (ORR) of 20% and a median progression-free survival of 5.5 months (95% CI, 2.9−6.9). Suppression of PI3K-AKT signaling results in induction of ER-dependent transcription, potentially limiting the response to single-agent PI3K/AKT inhibitors. We explored the hypothesis that simultaneous inhibition of AKT and ER signaling would enhance antitumor efficacy in AKT1m ER+ MBC.

Methods: In an expansion of this study, we administered oral AZD5363 400 mg twice daily, 4 days on 3 days off, and fulvestrant 500 mg, to AKT1m (detected in tumor tissue by local screening and/or plasma BEAMing) ER+ HER2– MBC pts, enrolled into a fulvestrant-naïve (FN) or fulvestrant-resistant (FR) cohort (max 24 pts/cohort). Key objectives included safety and efficacy by RECIST v1.1. We report results of a planned interim analysis conducted when 12 pts/cohort reached maturity for assessment of 24-week clinical benefit rate (CBR), defined as the percentage of responders plus those with stable disease (SD) ≥24 weeks.Data cut-off occurred in June 2017.

Results: At the time of analysis, 24 AKT1m pts (23 E17K, 1 E40K) had received treatment. FN had more visceral disease (83.3% vs 66.7%) and ER+/PR– status (25% vs 8.3%) than FR. Median number of prior anticancer regimens was 4.5 (range 1–9) and 6 (2–11) in FN and FR, respectively, with more chemotherapy (CT) and less hormone therapy (HT) exposure in FN vs FR [3 (0–5) vs 2 (0–6) and 2 (0–4) vs 4 (2–6) prior CT and HT, respectively]. Prior palbociclib was received by 1 (8.3%) and 4 (33.3%) pts in FN and FR, respectively. Clinical efficacy is detailed below; CBR was 33% and 42% in FN and FR, respectively (Table 1). There was 1 unconfirmed partial response in patients treated with prior palbociclib and 3 SD. At data cut-off, 18 pts had discontinued treatment: progressive disease, n=12; adverse events (AEs), n=2; other reasons, n=4. AEs were observed in all 24 pts, most commonly diarrhea (71%), nausea (63%), vomiting and decreased appetite (29%). Grade ≥3 AEs occurred in 13 (54%) pts, most frequently maculopapular rash (n=3), nausea, hyperglycemia and back pain (all n=2). Dose reduction due to AEs occurred in 3 pts.

Table 1. Clinical efficacy FNFREligible for interim data cut-off, n1212ORR, n (%)2 (17)4 (33)CBR, n (%)4 (33)5 (42)Confirmed response (complete/partial response), n (%)2 (17)4 (33)SD ≥24 weeks, n (%)2 (17)1 (8)

Conclusions: AZD5363 plus fulvestrant is clinically active in AKT1m ER+ MBC pts, including in pts with demonstrated prior resistance to fulvestrant. Comparatively lower efficacy was observed in the FN cohort; factors that may have potentially contributed (eg disease characteristics) will be explored. cfDNA and genomic data will also be presented.

Citation Format: Smyth LM, Oliveira M, Ciruelos E, Tamura K, El-Khoueiry A, Mita A, You B, Renouf DJ, Sablin M-P, Lluch A, Mayer IA, Bando H, Yamashita H, Ambrose H, de Bruin E, Carr TH, Corcoran C, Foxley A, Lindemann JPO, Maudsley R, Pass M, Rutkowski A, Schiavon G, Banerji U, Scaltriti M, Taylor BS, Chandarlapaty S, Baselga J, Hyman DM. AZD5363 in combination with fulvestrant in AKT1-mutant ER-positive metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-32.

Abstract P5-21-05: Withdrawn

This abstract was withdrawn by the authors.

The efficacy of larotrectinib (LOXO-101), a selective tropomyosin receptor kinase (TRK) inhibitor, in adult and pediatric TRK fusion cancers

LBA2501

Background: Larotrectinib is the first selective small-molecule pan-TRK inhibitor. TRK fusions appear oncogenic independent of tumor lineage, are widely distributed across cancers, and affect all ages. We present an integrated dataset from 3 studies intended to support regulatory approval. Methods: All NTRK fusion pts with RECIST measurable disease enrolled to the adult (NCT02122913, n=8) and pediatric (NCT02637687, n=12) phase I trials and adult/adolescent phase 2 trial (NCT02576431, n=35) were analyzed. TRK fusion status was determined by local testing prior to enrollment. Pts were dosed predominantly at 100mg BID on a continuous 28-day schedule. Primary objective was investigator-assessed overall response rate (ORR) per RECIST v1.1. Secondary endpoints included duration of response (DOR) and safety. Data were cut on 31-JAN-2017. Results: 55 TRK fusion pts (12 peds, 43 adult, range: 4 mo.-76 yrs) were enrolled (median priors=2). Fusions involved NTRK1 (n=25), NTRK2 (n=1), and NTRK3 (n=29), and 14 unique partners. 13 discrete tumor types were treated: salivary (12), sarcoma (10), infantile fibrosarcoma (7), lung (5), thyroid (5), colon (4), melanoma (4), cholangio (2), GIST (2), and other (4). For the 46 pts evaluated to date, the ORR was 78% (95% CI: 64%–89%) with responses in 12 unique tumor types. Responses are ongoing in 29/33 (88%) pts, excluding 3 peds pts whose DOR was censored at attempted curative resection. A median DOR has not been reached as the majority of responders remain on treatment without progression. The longest responder remains on treatment at 23 mos., 8 pts remain in response at >12 mos., and 16 pts at >6 mos. NTRK solvent front mutations were detected in all 4 pts to develop acquired resistance. The most common TEAEs were fatigue (30%), dizziness (28%), and nausea (28%). 5 (11%) pts required dose reductions. Conclusions: Larotrectinib has demonstrated consistent and durable antitumor activity in TRK fusion cancers, across a wide range of ages and tumor types, and was well-tolerated. Larotrectinib could be the first targeted therapy developed in a tissue type-agnostic manner, and the first developed simultaneously in adults and pediatrics. Clinical trial information: NCT02576431, NCT02122913, NCT02637687.

Efficacy of vemurafenib in patients (pts) with non-small cell lung cancer (NSCLC) with BRAFV600 mutation

9074

Background: BRAFV600 mutations occur in 1–2% of pts with NSCLC. We previously reported the efficacy of vemurafenib, a selective BRAFV600 inhibitor, in BRAF mutation-positive non-melanoma tumors (VE-BASKET study). We now present final data for the expanded NSCLC cohort. Methods: This open-label, histology-independent, phase 2 study included 6 prespecified cohorts (including NSCLC) plus one ‘all-others’ cohort. Pts received vemurafenib (960 mg bid) until disease progression or unacceptable toxicity. The primary endpoint was objective response rate (RECIST v1.1). Secondary endpoints included best overall response rate, duration of response (DoR), progression-free survival (PFS), and overall survival (OS). Because the pre-specified clinical benefit endpoint was met in the initial NSCLC cohort, the cohort was expanded. ClinicalTrials.gov identifier NCT01524978. Results: Database lock was 12 Jan 2017. Of 208 pts enrolled at 25 centers worldwide, 62 pts had NSCLC: median age 65 years; 56% male; 13% had no prior systemic therapy; 50% had ≥2 prior therapies. Responses were seen in previously treated and untreated pts (Table). The most common all-grade adverse event (AE) was nausea (40%); grade 3–5 AEs included keratoacanthoma (15%) and squamous cell carcinoma of the skin (15%). Six pts discontinued vemurafenib due to AEs; two had non-treatment-related fatal AEs. Conclusions: Vemurafenib showed evidence of encouraging efficacy in pts with NSCLC with BRAFV600 mutation, with prolonged PFS in previously untreated pts; median OS was not estimable due to ongoing responses. The safety profile of vemurafenib was similar to that seen in melanoma studies. Our results suggest a role for BRAF inhibition in NSCLC with BRAF mutations. Clinical trial information: NCT01524978. [Table: see text]

Discovery and prevalence of cancer-susceptibility germline mutations (Mts) in patients (Pts) with advanced renal cell carcinoma (aRCC)

4524

Background: About 5% of RCC is thought to be familial, but recent studies suggest this may be an underestimate (Int. J. Cancer;100:476). We studied the prevalence of germline cancer-susceptibility mts in pts with aRCC. Methods: Pts with aRCC (stage III or IV), unselected for suspicion of an inherited cancer syndrome, were offered germline testing for 76 cancer-associated genes between 10/2015 and 12/2016. Germline sequencing was done as part of MSK-IMPACT, a matched tumor-normal next-generation sequencing platform. Results: 203/213 pts accepted testing (median age 55, range 13-55) of whom 73% had clear cell RCC (ccRCC), 92% had metastases, 20% were early onset (≤46 yrs at diagnosis), 9% had a family history of RCC, 6% multifocal RCC at diagnosis, and 15% ≥2 primary malignancies. Pathogenic/likely pathogenic mts were found in 35 pts (17%): 12 (6%) with mts in genes associated with familial RCC; 10 (5%) mts in high/moderate penetrance genes not linked to RCC (Table).13 (6%) had mts in genes of low/uncertain penetrance or for autosomal recessive disease. Mts were present in 15% of ccRCC and 19% of non-ccRCC. Mts were not more common in pts with early onset, family history, multifocal RCC, or ≥2 malignancies (p>0.1 for each by Fisher’s exact test). Notably, 4/12 pts with mts in familial RCC genes did not meet the American College of Medical Genetics (ACMG) criteria for testing (1 each VHL, BAP1, SDHA, FH). Prevalence of CHEK2 mts was compared to population databases (ExAC); CHEK2 conferred a relative risk of 10.9 (p< 0. 002; CI=3.9-24.7) for RCC. Conclusions: 17% of aRCC pts had a germline mutation in a cancer-associated gene of which 33% of the high penetrance RCC germline mts were not identified using standard clinical criteria, providing rationale for broad testing. Once the increased risk is confirmed, CHEK2 should be included in RCC genetic testing. [Table: see text]

Vemurafenib in patients with BRAFV600 mutant glioma: A cohort of the histology-independent VE-basket study

2004

Background: Recurrent malignant gliomas (MG) are a universally fatal disease in desperate need of better therapies. Pleiomorphic xanthoastrocytomas (PXA) and juvenile pilocytic astrocytomas (JPA) typically have better outcomes, although when recurrent, also represent an aggressive disease with no proven effective chemotherapy. BRAFV600 alterations have been identified in a substantial proportion of gliomas, including glioblastoma (GBM), astrocytoma, PXA, and JPA. The phase 2, open-label, histology-independent VE-BASKET study of vemurafenib, a selective BRAFV600 kinase inhibitor, in patients with BRAF mutation-positive non-melanoma tumors, included those with gliomas in the ‘all-others’ cohort. We now report final data for patients with recurrent gliomas. Methods: Patients received vemurafenib (960 mg bid) until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed response rate; secondary endpoints included clinical benefit rate (confirmed complete or partial response or stable disease lasting ≥6 months), progression-free survival (PFS), overall survival (OS), and toxicity. ClinicalTrials.gov NCT01524978. Results: 24 patients (median age 32 years; 18 female, 6 male) with glioma were treated, including mg (n = 11; 6 GBM and 5 anaplastic astrocytoma [AA]), PXA (n = 7), anaplastic ganglioglioma (AG, n = 3), JPA (n = 2), and unknown (n = 1). In patients with mg (n = 11), best response included PR (n = 1; AA), SD (n = 5), PD (n = 3), and unknown (n = 2). Two patients with mg had durable SD lasting 12.9 months (GBM) and 14.9 months (AA). In patients with PXA (n = 7), best response included CR (n = 1), PR (n = 2), SD (n = 3), and PD (n = 1). Additionally, 1 patient with JPA and 1 with AG achieved a PR. The most frequent AEs included arthralgia (67%), melanocytic nevus (38%), palmar-plantar erythrodysesthesia (38%), photosensitivity reaction (38%) and alopecia (33%). Conclusions: Vemurafenib demonstrated activity in patients with BRAFV600 mutant glioma. The safety profile was similar to that seen in previous melanoma studies. Survival data will be presented. Clinical trial information: NCT01524978.

Somatic tumor profiling of DNA mismatch repair (MMR) deficient endometrial cancers (EC)

e17121

Background: Approximately 20% of EC have loss of MMR ( MSH2, MSH6, MLH1, PMS2) protein expression by immunohistochemistry (IHC). The majority have somatic MLH1/PMS2 loss, driven by MLH1 promoter hypermethylation. For the remaining patients (pts), germline testing for Lynch Syndrome (LS) is recommended. However, half do not have a corresponding germline mut. This is considered “Lynch-like syndrome” (LLS) & clinical management is challenging. We sought to determine if tumor profiling could identify somatic mut potentially underpinning loss of protein expression. Methods: Per institutional standard, all EC, regardless of age or family history undergo reflex LS screening with IHC for MMR protein expression. Pts consented to IRB approved protocols. Tumor-normal sequencing was performed via custom next-generation sequencing panel (MSK-IMPACT). Electronic medical records were reviewed. Results: 16 pt have completed tumor sequencing, median age 53 (35-83), 6 (38%) < 50 yrs at diagnosis. 2 had personal history of additional cancer (DCIS, ovary), none had first degree relative with colon or EC. A mix of EC histologies was represented: 10 endometrioid (all grades), 2 clear cell, 4 mixed. There were no serous cancers. There were median 58 mut (9-546), 14 (88%) had hyper or ultra mutated EC. 5 EC were driven by somatic POLE mut (3 known hotspot, 1 likely pathogenic), all ultra-mutated phenotype, resulting in multiple somatic MSH6 muts with isolated IHC MSH6 loss. 4 EC had MSH2/MSH6 IHC loss with corresponding double somatic mut in MSH2. 5 had one somatic mut corresponding to the MMR protein loss, assessment of LOH in these cases is pending. Two cases are unexplained: 40 yo with IHC MLH1 loss, 47mut; 69 yo, IHC MSH6 loss, 12 mut. In this cohort of LLS, somatic muts were frequently observed in ARID1A (13,81%), PTEN (10,63%) & PIK3CA(9,56%), in keeping with non serous histologies. Conclusions: In line with our prior report that pt with LLS had benign personal & family cancer histories compared with LS pts, we have identified that in 56% of LLS EC either POLE mut or double somatic MMR mut likely underpins the MMR IHC loss. As such, in these LLS EC cases, somatic tumor profiling may help to rule out LS. Further testing is ongoing to increase cohort size.

A prospective analysis of germline alterations (GA) in biliary tract cancer (BTC)

4085

Background: The incidence of hereditary cancer predisposition syndromes in patients (pts) with BTC is unknown. Cholangiocarcinoma has been reported in pts with germline mutations in BAP1, BRCA1/2, and mismatch repair genes. These associations are poorly characterized to date and the majority of pts do not undergo clinical germline analysis (CGA). Methods: Pts with BTC were offered consent to CGA between 01/2016 and 01/2017 under an IRB approved protocol (NCT01775072). Using the MSK-IMPACT platform, 76 genes associated with hereditary cancer predisposition were analyzed for germline variants and matched tumor samples were analysed for somatic alterations in > 340 genes. Demographic and clinical data were collected. Results: 78 patients were accrued: Intrahepatic = 52, extrahepatic = 13, gallbladder = 13. Median age at diagnosis was 57 years (range 21-80), 45 (58%) had a positive family history of cancer in at least one 1st degree or two 2nd degree relatives. 7 patients had a personal history of cancer. A pathogenic or likely pathogenic GA was identified in 16 pts (20%). (See table). Conclusions: Prospective analysis of GAs in pts with BTC, unselected by family history or age, revealed potentially actionable findings in 20% of pts. CGA in pts with BTC may benefit patients and their families in view of screening and therapeutic implications. [Table: see text]

Somatic mutations in homologous recombination pathway genes in ovarian cancer

5545

Background: 15% of patients with OC have a germline BRCA 1 / 2 mut & 6% of OC have a somatic BRCA 1/ 2 mut. Inhibitors of poly ADP ribose polymerase (PARPi) are approved in this setting. Data is evolving as to activity of PARPi in BRCA wild type OC with somatic homologous recombination (HR) gene deficiency. We sought to determine the prevalence of somatic alterations in HR genes in an unselected cohort of epithelial OC of any histologic type. Methods: From 03/2014-10/2016 patients consented to an IRB approved protocol for tumor-normal sequencing, via a custom next-generation sequencing panel (MSK-IMPACT) with return of results for tumor mut only. Muts in 14 HR genes ( ATM, BARD1, BRCA1, BRCA2, BRIP1, CHEK1, CHEK2, FANCA, MRE11, NBN, PALB2, PTEN, RAD51D, RAD51C) and p53were assessed. Statistics were analyzed using GraphPad Prism v. 6. Results: 260 tumors were sequenced; 156 (60%) high grade serous (HGS), 34 (13%) low grade serous (LGS), 34 (13%) clear cell, 10 (4%) mucinous, 8 (3%) endometrioid, 18 (7%) mixed/other histology. 151 (97%) of HGS and 24 (23%) of the remaining tumors harbored p53 mut. 48 (18%) somatic HR mut were identified. (Table 1) 26 HGS (17%) tumors and 22 (21%) of the remaining tumors harbored a HR gene mut (HGS vs other histology, p=0.4). Notably, 8 (24%) of clear cell cancers demonstrated HR gene muts (vs HGS, p=0.3). 18 (38%) of the identified muts in the overall cohort were in BRCA 1/2. There were no somatic HR gene muts identified in the mucinous OC, which were characterized by frequent p53 (90%) and KRAS(60%) muts. Conclusions: In this cohort of OC, 17% of tumors harbor somatic HR gene muts. The prevalence of HR somatic muts was similar in HGS vs other histologies, with the exception of mucinous OC. BRCA1/2 muts predominated, however 60% of identified muts were in other genes. Accrual is ongoing to increase histologic cohort sizes. Broad HR gene somatic mutational profiling may identify a wider cohort of OC patients with potential to benefit from PARPi therapy. [Table: see text]

First-in-class oral ERK1/2 inhibitor Ulixertinib (BVD-523) in patients with advanced solid tumors: Final results of a phase I dose escalation and expansion study

2508

Background: Aberrant MAPK pathway activation is known to be an oncogenic driver in many solid tumors, making ERK inhibition an attractive therapeutic strategy. Ulixertinib is an oral ERK1/2 inhibitor that demonstrated potent activity in vitro and tumor regression in BRAF and RAS mutant xenograft models. Methods: This multi-center phase I trial enrolled patients (pts) with advanced solid tumors. Dose escalation utilized an accelerated 3+3 design; expansion cohorts included BRAF or NRAS mutant melanoma and other BRAF or MEK mutant cancers. Study objectives were to characterize dose limiting toxicities (DLTs), maximum tolerated dose (MTD), toxicity profile, pharmacokinetics, pharmacodynamics and preliminary anti-tumor activity by RECIST 1.1. Results: A total of 135 pts were enrolled. Dose escalation enrolled 27 pts (10-900 mg BID) and established the MTD and recommended phase 2 dose (RP2D) of 600 mg BID. DLTs included rash, diarrhea, elevated AST, and elevated creatinine. Drug exposure was dose proportional up to the RP2D, which provided near-complete inhibition of ERK activity in whole blood. In the 108 pt expansion cohort, there were no drug related deaths; however, 32% of pts required a dose reduction. The most common adverse events were rash (49%), diarrhea (47%), fatigue (41%), and nausea (37%). In addition to 3 pts with partial responses during escalation (11%), an additional 9 of 83 (11%) evaluable pts at expansion had a partial response: 1 melanoma pt refractory to prior BRAFi/MEKi treatment, 3 NRAS mutant melanoma pts, 2 pts with BRAF V600E mutant lung cancers including response in brain metastases, 1 with BRAF V600E mutant glioblastoma multiforme, 1 with BRAF G469A head & neck cancer, and 1 with BRAFL485W gallbladder cancer. The duration of response ranged from 2 to 24+ months. Conclusions: Ulixertinib at 600 mg twice a day has an acceptable safety profile and has produced durable responses in pts with NRAS mutant melanoma, BRAF V600 and non-V600 mutant solid tumors including melanoma, glioblastoma multiforme, lung cancers with brain metastases, gallbladder and head & neck cancers. These data support further clinical development of ulixertinib. Clinical trial information: NCT01781429.

The efficacy of larotrectinib (LOXO-101), a selective tropomyosin receptor kinase (TRK) inhibitor, in adult and pediatric TRK fusion cancers

LBA2501

The full, final text of this abstract will be available at abstracts.asco.org at 7:30 AM (EDT) on Saturday, June 3, 2017, and in the Annual Meeting Proceedings online supplement to the June 20, 2017, issue of the Journal of Clinical Oncology. Onsite at the Meeting, this abstract will be printed in the Saturday edition of ASCO Daily News.

Safety and tolerability of the dual PI3K/mTOR inhibitor LY3023414 in combination with fulvestrant in treatment refractory advanced breast cancer patients

1064

Background: Thephosphatidylinositol 3-kinase (PI3K) /mammalian target of rapamycin (mTOR) pathway is frequently activated in breast cancer. LY3023414 (LY) is an oral ATP- competitive inhibitor that selectively and potently inhibits class I PI3K isoforms, mTOR, and DNA-PK. The recommended phase 2 dose (RP2D) of LY monotherapy was previously established to be 200 mg twice daily (BID). Here we present the safety and preliminary activity data of LY in combination with fulvestrant (F) for breast cancer patients (pts) as part of a multi-cohort Phase 1 study. Methods: Pts with advanced HR+, HER2- breast cancer refractory to standard treatment received 200 mg LY BID + 500 mg F (day 1 and 15, then once monthly). Eligible pts had measurable disease and baseline tumor tissue available. Primary objective was to determine a RP2D. Other objectives included assessment of pharmacokinetics (PK), antitumor activity, and biomarker analysis. Results: 9 pts received LY + F in the breast cancer expansion cohort. All pts had multiple lines of prior systemic therapy (range 3-12), including chemotherapy. Dose limiting toxicity was observed in one pt in the form of grade (Gr) 3 oral mucositis. Common possibly related adverse events included nausea (5 pts), vomiting (4 pts), oral mucositis (4 pts), decreased appetite (3 pts), fatigue (3 pts), mucosal inflammation (2 pts), and paresthesia (2 pts). No obvious impact of LY on F PK or of F on LY PK was observed. Median duration of treatment was 15 weeks (range 3-63). In the 6 pts evaluable for tumor response, there was 1 durable partial response according to RECIST (still on treatment for ≥11 months) and 4 further pts had a decrease in their target lesions for a disease control rate of 56%. The median progression-free survival for this cohort is 4.2 months (90% CI 1.8, NA). Of note, the partial response was observed in a pt harboring an activating PIK3CA mutation (H1047R). Further biomarker analysis is ongoing. Conclusions: The RP2D of LY in combination with F is 200mg BID and may cause tumor regression or stabilization in breast cancer pts. Clinical trial information: NCT01655225.

Integrating clinical pharmacy services into patient care in an early-phase clinical trial clinic

e18228

Background: Early phase clinical trials have broadened treatment options for patients with cancer. Expert management of these new therapies is essential to positive patient outcomes. At Memorial Sloan Kettering Cancer Center, the Developmental Therapeutic Center (DTC) satisfies this need. Oncology clinical pharmacists collaborate with other healthcare professionals to maximize the benefits of drug therapy and minimize toxicities. The purpose of this project is to describe the interventions from a clinical pharmacist assigned to the DTC. Methods: A clinical pharmacist joined DTC to serve adult patients with cancer undergoing clinical trials. The clinical pharmacist acted as a liaison between pharmacy team and medical team, and sees patients during their trial eligibility screening and follow-up visits. The interventions were documented by the clinical pharmacist in patients’ medical charts and email communications. All interventions during 1 month were retrospectively collected and categorized into supportive care optimization, protocol violation prevention, and operational. Results: The oncology clinical pharmacist was involved in 115 patient visits for trial eligibility screening or protocol follow-up. A total of 769 interventions were addressed including supportive care optimization (40.2%), protocol violation prevention (24.7%), and operational (35.1%). Conclusions: The oncology clinical pharmacist is actively engaged in many aspects of cancer care at the early phase trial clinic. Our results demonstrate the vital role of an oncology clinical pharmacist. The impact of these categorized intervention areas would require a formal outcome and cost-saving analysis. [Table: see text]

A phase II trial of enzalutamide in patients with androgen receptor positive (AR+) ovarian, primary peritoneal or fallopian tube cancer and one, two, or three prior therapies

TPS5610

Background: Approximately 75% of women with epithelial ovarian cancer (OC) present with advanced disease. Most of these women will ultimately recur and require life-long treatment for their cancer. Well tolerated therapies for treatment in the recurrent setting are needed. The AR is expressed in greater than 60% of cases of OC and is more prevalent than the estrogen or progesterone receptor. All past clinical studies of AR inhibition in OC have focused on unselected populations of heavily pretreated women; however preclinical data suggests that AR expression decreases in OC cells with increasing lines of therapy. Enzalutamide is a small molecule androgen receptor-antagonist that is FDA approved for treatment of prostate cancer and is currently being investigated as treatment for breast and ovarian cancer. Methods: This is a phase II, single-institution trial of enzalutamide 160mg po QD in patients with AR+ ovarian, fallopian tube or primary peritoneal cancer. Eligible patients must be found to have greater than or equal to 5% AR staining by IHC on FFPE tumor tissue and been treated with only 1,2 or 3 prior cytotoxic therapies. Patients must have RECIST 1.1 defined measurable disease. Enrolled patients are treated with enzalutamide until progression of disease or unacceptable toxicity. The primary endpoint is to estimate the proportion of women who achieve a complete or partial response by RECIST 1.1 criteria or survive progression free for at least 6 months. Secondary objectives include the retrieval of optional tumor biopsies at time of progression to evaluate the effect of enzalutamide on AR expression and to observe the effect of enzalutamide on serum testosterone and estradiol levels. This study will enroll 58 patients at Memorial Sloan Kettering Cancer Center and its regional sites. The study utilizes a safety lead-in phase and a two-stage design. The first patient enrolled in April 2015. The safety lead-in phase has been completed. The prespecified activity goal for the first stage was met; second stage accrual began in October 2016. Thus far, 35 patients have initiated treatment. Clinical trial information: NCT01974765.

Ado-trastuzumab emtansine in patients with HER2 mutant lung cancers: Results from a phase II basket trial

8510

Background: Human epidermal growth factor receptor 2 ( HER2, ERBB2) mutations occur in 2% of lung cancers, resulting in receptor dimerization and kinase activation with in vitro sensitivity to trastuzumab. Ado-trastuzumab emtansine is a HER2 targeted antibody drug conjugate linking trastuzumab with the anti-microtubule agent emtansine. Methods: Patients (pts) with HER2 mutant lung cancers were enrolled into a cohort of the basket trial of ado-trastuzumab emtansine in HER2amplified or mutant cancers, treated at 3.6mg/kg IV every 3 weeks. The primary endpoint was overall response rate (ORR) using RECIST v1.1. A Simon two stage optimal design was used with type I error rate under 2.7% (and a family wise error rate across baskets under 10%), power of 89%, H0 10%, H1 40%; the H0 will be rejected if 5 or more responses are observed in 18 pts. Other endpoints include duration of response (DOR), progression-free survival (PFS) and toxicity. HER2 testing was performed on tumor tissue by next generation sequencing (NGS), fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC). Results: The cohort completed accrual with 18 pts treated. The median age was 63 (range 47-74 years), 72% were female, 39% were never smokers and all had adenocarcinomas. The median lines of prior systemic therapy was 2 (range 0-4). ORR was 33% (5/15 confirmed, 95% CI 12-62%) not including a partial response awaiting confirmation and 3 pts pending response evaluation. Median DOR was not reached (range 3 to 7+ mo), median PFS was 4mo (95% CI 3mo-not reached). Toxicities were mainly grade 1 or 2 including infusion reaction, thrombocytopenia and transaminitis, there were no dose reductions or treatment related deaths. There were 10 (56%) exon 20 insertions and 8 (44%) point mutations; responders were seen across mutation subtypes (A775_G776insYVMA, G776delinsVC, V659E, S310F). HER2amplification was negative for all pts by NGS and positive for 1 of 12 pts by FISH. There was no IHC3+ in 10 pts tested. Conclusions: Ado-trastuzumab emtansine is active and well tolerated in pts with HER2 mutant lung cancers. This study has met its primary endpoint. Further development in a multicenter study is warranted. Clinical trial information: NCT02675829.

Circulating tumor cells and genomic profiling of patients with ERBB2 mutant, HER2 non-amplified metastatic breast cancer treated with neratinib

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Background: ERBB2 mutations in the absence of gene amplification are rare, with an incidence of 2-4%. Neratinib is a HER2/EGFR tyrosine kinase inhibitor being evaluated for use in ERBB2 mutated breast cancer. Neratinib has been found to have clinical activity on heavily pre-treated ERBB2 mutant breast cancer patients. We are evaluating the response and genomic profiles of 3 postmenopausal patients with metastatic ERBB2 mutant/non-amplified breast cancer receiving neratinib and fulvestrant NCT01953926, NCT01670877. Methods: Samples were collected at different points during treatment and CTCs were identified. Other representative cells were tracked but not classified as CTCs. CD45-CK+ cells with cytoplasmic and/or nuclear apoptosis were defined as CTC-Apoptotic. CD45- cells expressing little to no CK but otherwise meeting morphological criteria for CTCs are CTC-LowCK. CD45-CK+ cells with small nuclear size are CTC-SmallCK. Single CTCs will be analyzed using whole genome copy number variation to determine chromosomal alterations. Results: The patients had an average of 4.7 lines of therapy for metastatic disease before neratinib. Two had stable disease and one had progression. The patient who progressed had a rise in the number of CTCs from 37 to 52 cells/ml and drop in apoptotic cells from 5 to 0 cells/ml. Conclusions: The high CTC count of the patient who progressed may suggest more aggressive disease. The drop in the apoptotic cell count may correlate with a failure to respond to therapy. Samples have been sent for copy number variation profiling. The goal is to identify any genomic amplifications or deletions associated with clinical response and progression after targeted therapy. We hope to demonstrate the timeframe of tumor evolution in response to therapy and provide a framework for the use of fluid biopsies to monitor disease progression. [Table: see text]

Abstract P3-03-03: An acquired HER2 T798I gatekeeper mutation induces resistance to neratinib in a patient with HER2 mutant-driven breast cancer

ERBB2, the gene encoding HER2, is mutated in 2-4% of breast cancers. The HER2 irreversible tyrosine kinase inhibitor (TKI) neratinib has shown clinical activity against breast cancer cells harboring HER2 activating mutations. Here, we report for the first time an acquired gatekeeper HER2T798I mutation in a patient with HER2-mutant breast cancer after an initial exceptional response to neratinib.

A patient with ER+/PR+/HER2-negative invasive lobular breast cancer progressing on standard therapy was found to harbor a L869R kinase domain mutation in HER2. HER2L869R is homologous to the known activating mutation EGFRL861R/Q. MCF10A breast epithelial cells expressing HER2L869R displayed enhanced HER2-mediated signaling and were resistant to lapatinib and trastuzumab but sensitive to neratinib. The patient was enrolled in the phase II SUMMIT trial (NCT01953926) and treated with neratinib, achieving a partial response lasting 16 months before developing progression. Next gen sequencing of DNA from both a new skin metastasis and plasma cell-free DNA (cfDNA) identified HER2L869R (8.7% cfDNA), whereas a novel HER2T798I mutation was detected only in plasma at 1.3%. Deep sequencing of pre-therapy tumor tissue and plasma did not detect HER2T798I, suggesting that this mutation arose upon resistance. HER2T798I has not been reported in TCGA, COSMIC, or among plasma samples from 17,345 cancer patients subjected to digital DNA sequencing using the Guardant360 assay.

HER2T798I is homologous to the EGFRT790M, KITT670I and BCR-ABLT315I gatekeeper mutations known to mediate resistance to erlotinib/gefitinib and imatinib. To examine if HER2T798I mediates resistance to neratinib, we employed biochemical and biological assays and molecular modeling of wild-type (WT) HER2 and HER2T798I. Structural modeling showed the increased bulk of the isoleucine at position 798 would result in a steric clash with neratinib, thus reducing drug binding. We stably expressed HER2WT, HER2T798I, HER2L869R and HER2L869R/T798I in MCF10A cells and NR6 mouse fibroblasts. Neratinib (10-100 nM) blocked HER2-mediated signaling in cells expressing HER2WT or HER2L869R but did not in cells expressing HER2T798I. The EGFR irreversible TKI osimertinib (100 nM), which isselective for mutant EGFR (including EGFRT790M) and approved for treatment of NSCLC expressing EGFRT790M, failed to inhibit HER2WT, HER2L869R or HER2T798I. In contrast, either the EGFR/HER2 irreversible TKI afatinib or AZ5104, a metabolite of osimertinib, strongly blocked signaling induced by HER2WT, HER2L869R or HER2T798I. Cells expressing HER2T798M displayed a significantly higher IC50 to neratinib than cells expressing HER2WT, whereas afatinib or AZ5014 were very active against all cells (IC50&lt;10 nM).

Conclusions: The acquisition of a T798I gatekeeper mutation in HER2 upon development of clinical resistance to neratinib in a breast cancer with an initial activating mutation in HER2 strongly suggests that HER2L869R is a driver mutation. We speculate that HER2T798I may arise as a secondary mutation following response to effective HER2 TKIs in other cancers with HER2 activating mutations. Certain irreversible EGFR inhibitors may be effective in patients with HER2-driven breast cancer resistant to neratinib.

Citation Format: Hanker AB, Red Brewer M, Sheehan JH, Koch JP, Lanman R, Hyman DM, Cutler, Jr. RE, Lalani AS, Cross D, Lovly CM, Meiler J, Arteaga CL. An acquired HER2 T798I gatekeeper mutation induces resistance to neratinib in a patient with HER2 mutant-driven breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-03.