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Purpose: The identification of actionable oncogenic alterations has enabled targeted therapeutic strategies for subsets of patients with advanced malignancies, including lung adenocarcinoma (LUAD). We sought to assess the frequency of known drivers and identify new candidate drivers in a cohort of LUAD from patients with minimal smoking history. Experimental Design: We performed genomic characterization of 103 LUADs from patients with ≤10 pack-year smoking history. Tumors were subjected to targeted molecular profiling and/or whole-exome sequencing and RNA sequencing in search of established and previously uncharacterized candidate drivers. Results: We identified an established oncogenic driver in 98 of 103 tumors (95%). From one tumor lacking a known driver, we identified a novel gene rearrangement between OCLN and RASGRF1. The encoded OCLN-RASGRF1 chimera fuses the membrane-spanning portion of the tight junction protein occludin with the catalytic RAS-GEF domain of the RAS activator RASGRF1. We identified a similar SLC4A4-RASGRF1 fusion in a pancreatic ductal adenocarcinoma cell line lacking an activating KRAS mutation and an IQGAP1-RASGRF1 fusion from a sarcoma in The Cancer Genome Atlas. We demonstrate these fusions increase cellular levels of active GTP-RAS, induce cellular transformation, and promote in vivo tumorigenesis. Cells driven by RASGRF1 fusions are sensitive to targeting of the RAF-MEK-ERK pathway in vitro and in vivo. Conclusions: Our findings credential RASGRF1 fusions as a therapeutic target in multiple malignancies and implicate RAF-MEK-ERK inhibition as a potential treatment strategy for advanced tumors harboring these alterations. See related commentary by Moorthi and Berger, p. 2983

Purpose: MET inhibitors can be effective therapies in patients with MET exon 14 (METex14) mutant non–small cell lung cancer (NSCLC). However, long-term efficacy is limited by the development of drug resistance. In this study, we characterize acquired amplification of wild-type (WT) KRAS as a molecular mechanism behind crizotinib resistance in three cases of METex14-mutant NSCLC and propose a combination therapy to target it. Experimental Design: The patient-derived cell line and xenograft (PDX) DFCI358 were established from a crizotinib-resistant METex14-mutant patient tumor with massive focal amplification of WT KRAS. To characterize the mechanism of KRAS-mediated resistance, molecular signaling was analyzed in the parental cell line and its KRAS siRNA-transfected derivative. Sensitivity of the cell line to ligand stimulation was assessed and KRAS-dependent expression of EGFR ligands was quantified. Drug combinations were screened for efficacy in vivo and in vitro using viability and apoptotic assays. Results: KRAS amplification is a recurrent genetic event in crizotinib-resistant METex14-mutant NSCLC. The key characteristics of this genetic signature include uncoupling MET from downstream effectors, relative insensitivity to dual MET/MEK inhibition due to compensatory induction of PI3K signaling, KRAS-induced expression of EGFR ligands and hypersensitivity to ligand-dependent and independent activation, and reliance on PI3K signaling upon MET inhibition. Conclusions: Using patient-derived cell line and xenografts, we characterize the mechanism of crizotinib resistance mediated by KRAS amplification in METex14-mutant NSCLC and demonstrate the superior efficacy of the dual MET/PI3K inhibition as a therapeutic strategy addressing this resistance mechanism.

Oncogenic mutations in the epidermal growth factor receptor (EGFR) are identified in a subset of non-small cell lung carcinomas (NSCLC). These alterations lead to constitutive EGFR activation and upregulation of pathways promoting cell survival and proliferation. The development of small molecule inhibitors of EGFR has transformed the care of patients with advanced EGFR-mutant NSCLC. We review here the clinical development and activity of the third-generation EGFR inhibitor osimertinib in the advanced and adjuvant settings. As with other targeted therapies, resistance to osimertinib is common and limits the efficacy of this agent. Here we present an overview of reported acquired resistance mechanisms and potential therapeutic strategies to overcome resistance. The heterogeneity of resistance mechanisms (including secondary EGFR mutations and diverse EGFR-independent alterations) presents a major therapeutic challenge in EGFR-mutant NSCLC.

Background Expert knowledge is often shared among multidisciplinary academic teams at tumor boards (TBs) across the country, but these conversations exist in silos and do not reach the wider oncology community. Objective Using an oncologist-only question and answer (Q&A) website, we sought to document expert insights from TBs at National Cancer Institute–designated Comprehensive Cancer Centers (NCI-CCCs) to provide educational benefits to the oncology community. Methods We designed a process with the NCI-CCCs to document and share discussions from the TBs focused on areas of practice variation on theMednet, an interactive Q&A website of over 13,000 US oncologists. The faculty translated the TB discussions into concise, non–case-based Q&As on theMednet. Answers were peer reviewed and disseminated in email newsletters to registered oncologists. Reach and engagement were measured. Following each Q&A, a survey question asked how the TB Q&As impacted the readers’ practice. Results A total of 23 breast, thoracic, gastrointestinal, and genitourinary programs from 16 NCI-CCC sites participated. Between December 2016 and July 2021, the faculty highlighted 368 questions from their TBs. Q&As were viewed 147,661 times by 7381 oncologists at 3515 institutions from all 50 states. A total of 277 (75%) Q&As were viewed every month. Of the 1063 responses to a survey question on how the Q&A affected clinicians’ practices, 646 (61%) reported that it confirmed their current practice, 163 (20%) indicated that a Q&A would change their future practice, and 214 (15%) reported learning something new. Conclusions Through an online Q&A platform, academics at the NCI-CCCs share knowledge outside the walls of academia with oncologists across the United States. Access to up-to-date expert knowledge can reassure clinicians’ practices, significantly impact patient care in community practices, and be a source of new knowledge and education.

NRG1 rearrangements are oncogenic drivers that are enriched in invasive mucinous adenocarcinomas (IMAs) of the lung. The oncoprotein binds ERBB3-ERBB2 heterodimers and activates downstream signaling, supporting a therapeutic paradigm of ERBB3/ERBB2 inhibition. As proof of concept, a durable response was achieved with anti-ERBB3 monoclonal antibody therapy (GSK2849330) in an exceptional responder with an NRG1-rearranged IMA on a phase 1 trial (NCT01966445). In contrast, response was not achieved with anti-ERBB2 therapy (afatinib) in four NRG1-rearranged IMA patients (including the index patient post-GSK2849330). While in vitro data supported the use of either ERBB3 or ERBB2 inhibition, these clinical results were consistent with more profound anti-tumor activity and downstream signaling inhibition with anti-ERBB3 versus anti-ERBB2 therapy in an NRG1-rearranged patient-derived xenograft model. Analysis of 8,984 and 17,485 tumors in The Cancer Genome Atlas and MSK-IMPACT datasets, respectively, identified NRG1 rearrangements with novel fusion partners in multiple histologies, including breast, head and neck, renal, lung, ovarian, pancreatic, prostate, and endometrial cancers.

9057 Background: In the registrational phase 2 CodeBreaK 100 trial, sotorasib demonstrated a response rate of 37.1% with median duration of 10.0 months, a median progression-free survival of 6.8 months, and a tolerable safety profile in patients with pretreated KRAS p.G12C mutated NSCLC. Patients received a median of 2 prior lines of therapy. Here, we report PRO measures of health-related quality of life (QoL), physical functioning, and key lung cancer symptoms from this trial. Methods: Eligible patients had KRAS p.G12C mutated advanced NSCLC and received prior standard therapies. Sotorasib was given at an oral daily dose of 960 mg with 21-day treatment cycles until disease progression. Disease-related symptoms and health-related QoL were evaluated as exploratory endpoints on day 1 of each cycle from baseline to discontinuation, using the European Organization for Research and Treatment of Cancer Quality-of-life Questionnaire Core 30 (EORTC QLQ-C30) and its lung cancer module, EORTC QLQ-LC13. The single item, 5-point scale GP5, of the Functional Assessment of Cancer Therapy-General version was used to evaluate the impact of side effects. Predefined analyses included change from baseline using descriptive statistics and mixed model for repeated measures for global health status/QoL, physical functioning, and key lung cancer symptoms of cough, dyspnea and chest pain. Results: Of 126 patients enrolled, compliance rates for each of the questionnaires were high throughout the study ( > 70%). Data up to cycle 11 (where n > 20) are presented. EORTC QLQ-C30 global health status/QoL and physical functioning were maintained over time (least-square mean changes ranged from -3.5 to 0.2 and 0.1 to 3.9, respectively). EORTC QLQ-C30 symptoms of fatigue, nausea/vomiting, pain, dyspnea, insomnia, appetite loss, and constipation were stable or improved. Similarly, key lung cancer-related symptoms, as measured by EORTC QLQ-LC13, remained stable or improved from baseline, with the greatest least-square mean change of -11.2 (95% Cl: -16.2, -6.1) for cough, -4.9 (95% Cl: -10.3, 0.4) for chest pain, and -3.4 (95% Cl: -7.8, 1.0) for dyspnea. Most patients reported on the GP5 that they were “not at all” (54.2%-79.2%) or “a little bit” (8.3%-33.3%) bothered by side effects from sotorasib, with 0%-7.4% reporting being bothered as “quite a bit” and 0% as “very much”. Conclusions: In patients from the single-arm phase 2 trial of sotorasib, PRO measures suggested maintenance or improvement of global health status/QoL, physical functioning, and the severity of key lung cancer-related symptoms, including cough, dyspnea, and chest pain. Self-reported side effect bother was minimal. These data, together with the encouraging efficacy and safety profiles, strongly support the use of sotorasib in this population. Clinical trial information: NCT03600883.

SummaryWe conducted a large-scale functional genetic study to characterize mechanisms of resistance to ALK inhibition in ALK-dependent lung cancer cells. We identify members of known resistance pathways and additional putative resistance drivers. Among the latter were members of the P2Y purinergic receptor family of G-protein-coupled receptors (P2Y1, P2Y2, and P2Y6). P2Y receptors mediated resistance in part through a protein-kinase-C (PKC)-dependent mechanism. Moreover, PKC activation alone was sufficient to confer resistance to ALK inhibitors, whereas combined ALK and PKC inhibition restored sensitivity. We observed enrichment of gene signatures associated with several resistance drivers (including P2Y receptors) in crizotinib-resistant ALK-rearranged lung tumors compared to treatment-naive controls, supporting a role for these identified mechanisms in clinical ALK inhibitor resistance.

272 Background: Expert knowledge is often shared among academic oncologists at tumor boards (TBs) at National Cancer Institute Designated Cancer Centers (NCI-CCs), but not documented or made accessible to community oncologists. Using an oncologist-only question and answer (Q&A) website, we sought to disseminate expert insights from TBs at NCI-CCs to provide educational benefit to the oncology community. Methods: A process was designed with faculty at 11 NCI-CCs to document and share discussions from TBs focused on areas of clinical complexity and practice variation on theMednet.org, an interactive Q&A website of over 8,700 US oncologists. One faculty member from each TB was selected as a site leader. She or he distilled discussions about patient management from the TB into a question that addressed the clinical situation being discussed. After the question was posted, faculty at the participating NCI-CCs were asked to answer the question on theMednet. Answers were peer reviewed, indexed, stored and disseminated via email newsletters to registered oncologists. Community engagement was measured by Q&A page views, upvotes of Q&A, and poll participation. Results: A total of 15 Breast, Thoracic, and Gastrointestinal programs from 11 NCI-CCs participated. Between 12/2016 and 5/2019, faculty highlighted 146 questions from their TBs. Q&A were viewed 43,291 times by 3,585 oncologists including 2,264 community oncologists. One hundred and eighty-four answers are posted by 56 academic physicians and peer reviewed by 76 academic physicians. One hundred and eighty-five publications were cited. Community oncologists upvoted Q&A 808 times and voted in 45 polls related to the questions 1,667 times. Viewership of NCI-CC Q&A increased by 419% over time. Q&A were repeatedly searched and viewed, with 90% of all TB Q&A viewed every month. Conclusions: Via the online Q&A theMednet platform, NCI-CC providers effectively made expert knowledge easily accessible to community oncologists across the US. Timely access to evidence based recommendations from expert faculty can inform future practice choices in the community. [Table: see text]

Tumors put in a vulnerable position Cancer cells often display alterations in metabolism that help fuel their growth. Such metabolic “rewiring” may also work against the cancer cells, however, by creating new vulnerabilities that can be exploited therapeutically. A variety of human tumors show changes in methionine metabolism caused by loss of the gene coding for 5-methylthioadenosine phosphorylase (MTAP). Mavrakis et al. and Kryukov et al. found that the loss of MTAP renders cancer cell lines sensitive to growth inhibition by compounds that suppress the activity of a specific arginine methyltransferase called PRMT5. Conceivably, drugs that inhibit PRMT5 activity could be developed into a tailored therapy for MTAP-deficient tumors. Science , this issue pp. 1208 and 1214

Haploinsufficiency for ribosomal protein genes has been implicated in the pathophysiology of Diamond-Blackfan anemia (DBA) and the 5q− syndrome, a subtype of myelodysplastic syndrome. The p53 pathway is activated by ribosome dysfunction, but the molecular basis for selective impairment of the erythroid lineage in disorders of ribosome function has not been determined. We found that p53 accumulates selectively in the erythroid lineage in primary human hematopoietic progenitor cells after expression of shRNAs targeting RPS14, the ribosomal protein gene deleted in the 5q− syndrome, or RPS19, the most commonly mutated gene in DBA. Induction of p53 led to lineage-specific accumulation of p21 and consequent cell cycle arrest in erythroid progenitor cells. Pharmacologic inhibition of p53 rescued the erythroid defect, whereas nutlin-3, a compound that activates p53 through inhibition of HDM2, selectively impaired erythropoiesis. In bone marrow biopsies from patients with DBA or del(5q) myelodysplastic syndrome, we found an accumulation of nuclear p53 staining in erythroid progenitor cells that was not present in control samples. Our findings indicate that the erythroid lineage has a low threshold for the induction of p53, providing a basis for the failure of erythropoiesis in the 5q− syndrome, DBA, and perhaps other bone marrow failure syndromes.

9069Background: Non-small cell lung cancers (NSCLC) harboring METex14 activating mutations can respond dramatically to treatment with MET TKIs, but the mechanisms of acquired resistance to these th...

Lung adenocarcinomas harboring activating mutations in the epidermal growth factor receptor (EGFR) represent a common molecular subset of non-small cell lung cancer (NSCLC) cases. EGFR mutations predict sensitivity to EGFR tyrosine kinase inhibitors (TKIs) and thus represent a dependency in NSCLCs harboring these alterations, but the genetic basis of EGFR dependence is not fully understood. Here, we applied an unbiased, ORF-based screen to identify genetic modifiers of EGFR dependence in EGFR-mutant NSCLC cells. This approach identified 18 kinase and kinase-related genes whose overexpression can substitute for EGFR in EGFR-dependent PC9 cells, and these genes include seven of nine Src family kinase genes, FGFR1, FGFR2, ITK, NTRK1, NTRK2, MOS, MST1R, and RAF1. A subset of these genes can complement loss of EGFR activity across multiple EGFR-dependent models. Unbiased gene-expression profiling of cells overexpressing EGFR bypass genes, together with targeted validation studies, reveals EGFR-independent activation of the MEK-ERK and phosphoinositide 3-kinase (PI3K)-AKT pathways. Combined inhibition of PI3K-mTOR and MEK restores EGFR dependence in cells expressing each of the 18 EGFR bypass genes. Together, these data uncover a broad spectrum of kinases capable of overcoming dependence on EGFR and underscore their convergence on the PI3K-AKT and MEK-ERK signaling axes in sustaining EGFR-independent survival.

Chemotherapy-induced peripheral neurotoxicity is a major problem because it represents the dose-limiting side effect of a significant number of antineoplastic drugs, such as vinca alkaloids. Hereditary neuropathies usually predispose to severe vincristine neurotoxicity. Here, we report the case of a 56-year-old man with Machado-Joseph disease, also known as spinocerebellar ataxia type 3, treated with a vinca alkaloid without exacerbation of neurological symptoms.

An understanding of driver genetic events in tumorigenesis has led to the development of targeted therapies with clinical benefit for subsets of patients with melanoma, non-small cell lung cancer, and other malignancies. The identification of new cancer vulnerabilities may provide additional therapeutic opportunities for malignancies refractory to standard treatments and may expand the use of targeted therapies to a broader patient population. To identify new cancer vulnerabilities and associated genetic features, we have integrated insights about recurrent genetic alterations (from the Cancer Cell Line Encyclopedia) with cancer cell line dependencies identified from genome-scale RNA interference (from Project Achilles). Using this approach, we find that cancer cell lines harboring a highly-recurrent alteration (homozygous deletion of the gene encoding methylthioadenosine phosphorylase or MTAP) show selective dependence on protein arginine methyltransferase 5 (PRMT5) and its binding partner WDR77, core components of the methylosome. Homozygous loss of MTAP occurs as a passenger event in cancer due to its proximity to the commonly-deleted tumor suppressor gene CDKN2A. MTAP is lost in >40% of glioblastomas and in 25-30% of melanomas, urothelial carcinomas, and pancreatic adenocarcinomas (in addition to other cancers). MTAP cleaves methylthioadenosine (MTA) to generate precursor substrates for methionine and adenine salvage pathways, which are compromised with MTAP loss. While MTAP deletion in cancer has long been recognized as a potential vulnerability (as tumors with MTAP loss are dependent on de novo purine synthesis), therapeutic strategies to exploit MTAP loss have not been successfully implemented. Our findings credential PRMT5 as a previously-unrecognized potential therapeutic target in MTAP-deleted cancers. We have performed mechanistic studies to confirm a role for MTAP in modulating sensitivity to genetic depletion of PRMT5 or WDR77. Furthermore, we propose a mechanism by which homozygous MTAP deletion confers a selective dependency on PRMT5 and WDR77. We show that loss of MTAP leads to increased intracellular levels of MTA, which in turn specifically inhibits the catalytic activity of PRMT5. Since PRMT5 activity is essential for cell viability, MTAP-deleted cells may have some degree of basal inhibition of PRMT5 activity that confers heightened sensitivity to further reduction in PRMT5 activity with gene depletion. Given the frequency of homozygous MTAP loss in cancer, our findings suggest a potential role for PRMT5 inhibition in multiple malignancies, either as a single agent or possibly in combination with other therapies. As MTAP loss is not mutually exclusive of oncogenic drivers in cancer (such as activating BRAF mutations in melanoma or EGFR mutations in lung cancer), it may theoretically be possible to combine PRMT5 inhibition with targeting of oncogenic drivers in an effort to augment anti-tumor activity and possibly delay or prevent the emergence of drug resistance. Citation Format: Frederick H. Wilson. PRMT5 as a therapeutic target in MTAP-deleted cancers [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr IA24.