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Background Immune checkpoint inhibitors have shown limited clinical benefits in MSS-CRC; dual targeting of non-redundant pathways may enhance antitumor immune response. In a phase I/II, multicenter, open-label study, the anti-PD-L1 antibody durvalumab (D) was combined with monalizumab (M), an IgG4 mAb that blocks NKG2A binding to HLA-E to reduce inhibition of NK and CD8+ T cells. The combination (D+M) was well tolerated and showed encouraging activity in heavily pretreated pts with advanced MSS-CRC. In a dose-exploration cohort, D+M was assessed in combination with standard of care (SOC) chemotherapy and bevacizumab, an anti-VEGF agent, as first-line therapy for advanced/metastatic MSS-CRC. Methods Eligible pts had histologically defined MSS-CRC, regardless of RAS/RAF mutational status, ECOG 0–1 and no prior systemic therapy. They received durvalumab 1500mg Q4W, monalizumab 750mg Q2W, modified FOLFOX6 (folinic acid, fluorouracil, and oxaliplatin) Q2W and bevacizumab 5mg/kg Q2W until end of treatment; dose modifications were allowed according to SOC practice except during the DLT evaluation period. The primary endpoint was safety and tolerability of D+M with FOLFOX6 and bevacizumab; secondary endpoints included antitumor activity. Results As of Mar 25, 2019, 18 pts were enrolled with median follow-up of 6.2 months. Monalizumab-related adverse events (AEs) occurred in 13 (72%), serious in 1 (6%; embolism). Durvalumab-related AEs occurred in 14 (78%; none serious). All pts had chemotherapy-related AEs, serious in 1 (6%; febrile neutropenia) and 10 (56%) had bevacizumab-related AEs, serious in 2 (11%; embolism and febrile neutropenia). There were no grade 5 or dose-limiting toxicities. At 16 weeks, 17 pts were evaluable for response; 9 (53%) had partial responses (7 confirmed, 2 unconfirmed), 6 (35%) had stable disease and 2 (12%) had progressive disease; there were no complete responses. Median time to response for the 7 confirmed responders was 15.4 weeks; median duration of response was not yet reached. Conclusions First-line D+M combined with SOC showed manageable safety and preliminary activity in pts with advanced/metastatic MSS-CRC. Accrual is complete. Clinical trial identification NCT02671435. Editorial acknowledgement Medical writing support was provided by Hashem Dbouk, PhD, of Cirrus Communications (Lyndhurst, NJ), an Ashfield company, and was funded by AstraZeneca. Legal entity responsible for the study AstraZeneca. Funding AstraZeneca. Disclosure J.C. Bendell: Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Gilead; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Genentech/Roche; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: BMS; Advisory / Consultancy, Research grant / Funding (institution): Five Prime; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Lilly; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Merck; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: AstraZeneca; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Celgene; Research grant / Funding (institution): EMD Serono; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Taiho; Advisory / Consultancy, Research grant / Funding (institution): MacroGenics; Advisory / Consultancy, Research grant / Funding (institution): GSK; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Novartis; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: OncoMed; Advisory / Consultancy, Research grant / Funding (institution): LEAP; Advisory / Consultancy, Research grant / Funding (institution): TG Therapeutics; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: BI; Advisory / Consultancy, Research grant / Funding (institution): Daiichi Sankyo; Advisory / Consultancy, Research grant / Funding (institution): Bayer; Advisory / Consultancy, Research grant / Funding (institution): Incyte; Advisory / Consultancy, Research grant / Funding (institution): Apexigen; Research grant / Funding (institution): Koltan; Research grant / Funding (institution): SynDevRex; Research grant / Funding (institution): Forty Seven; Research grant / Funding (institution): AbbVie; Advisory / Consultancy, Research grant / Funding (institution): Array; Research grant / Funding (institution): Onyx; Advisory / Consultancy, Research grant / Funding (institution): Sanofi; Research grant / Funding (institution): Takeda; Research grant / Funding (institution): Eisai; Research grant / Funding (institution): Celldex; Advisory / Consultancy, Research grant / Funding (institution): Agios; Research grant / Funding (institution): Cytomx; Research grant / Funding (institution): Nektar; Research grant / Funding (institution), Travel / Accommodation / Expenses: ARMO; Research grant / Funding (institution): Boston Biomedical; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Ipsen; Advisory / Consultancy, Research grant / Funding (institution): Merrimack; Research grant / Funding (institution): Tarveda; Research grant / Funding (institution): Tyrogenex; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Oncogenex; Research grant / Funding (institution): Marshall Edwards; Research grant / Funding (institution): Pieris; Research grant / Funding (institution): Mersana; Research grant / Funding (institution): Calithera; Research grant / Funding (institution): Blueprint; Research grant / Funding (institution): Evelo; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Forma; Research grant / Funding (institution): Merus; Research grant / Funding (institution): Jacobio; Research grant / Funding (institution): Effector; Research grant / Funding (institution): Novocare; Research grant / Funding (institution): Arrys; Research grant / Funding (institution): Tracon; Research grant / Funding (institution): Sierra; Advisory / Consultancy, Research grant / Funding (institution): Innate; Advisory / Consultancy, Research grant / Funding (institution): Arch Oncology; Advisory / Consultancy, Research grant / Funding (institution): Prelude Oncology; Research grant / Funding (institution): Unum Therapeutics; Research grant / Funding (institution): Vyriad; Research grant / Funding (institution): Harpoon; Research grant / Funding (institution): ADC; Advisory / Consultancy, Research grant / Funding (institution): Amgen; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Millennium; Research grant / Funding (institution): Imclone; Research grant / Funding (institution): Acerta Pharma; Research grant / Funding (institution): Rgenix; Research grant / Funding (institution): Bellicum; Advisory / Consultancy: Phoenix Bio; Advisory / Consultancy: Cyteir; Advisory / Consultancy: Molecular Partners; Advisory / Consultancy: Innate; Advisory / Consultancy: Torque; Advisory / Consultancy: Tizona; Advisory / Consultancy: Janssen; Advisory / Consultancy: Tolero; Advisory / Consultancy: TD2 (Translational Drug Development); Advisory / Consultancy: Seattle Genetics; Advisory / Consultancy: Moderna Therapeutics; Advisory / Consultancy: Tanabe Research Laboratories; Advisory / Consultancy: Beigene; Advisory / Consultancy: Continuum Clinical; Advisory / Consultancy: Kyn. J. Naidoo: Research grant / Funding (institution): Merck; Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy: BMS. X. Li: Full / Part-time employment: AstraZeneca. P. Kourtesis: Shareholder / Stockholder / Stock options, Full / Part-time employment: AstraZeneca. S.E. Abdullah: Travel / Accommodation / Expenses, Shareholder / Stockholder / Stock options, Full / Part-time employment: AstraZeneca. S. Patel: Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy, Research grant / Funding (institution): Bristol-Myers Squibb; Advisory / Consultancy: Illumina; Advisory / Consultancy: Nektar; Advisory / Consultancy: Tempus; Research grant / Funding (institution): Eli Lilly; Research grant / Funding (institution): Fate; Research grant / Funding (institution): Incyte; Research grant / Funding (institution): Merck; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Roche/Genentech; Research grant / Funding (institution): Xcovery; Research grant / Funding (institution): Fate Therapeutics; Research grant / Funding (institution): Genocea; Research grant / Funding (institution): Iovance. All other authors have declared no conflicts of interest.

Background A novel approach to differentiate somatic vs. germline BRCA1/2 mutations in cfDNA using a beta binomial model (AACR 2018, abst #4272) may enable identification of pts with advanced GI tumors who are likely to benefit from a PARP inhibitor. The results from the GOZILA study, the Nationwide Cancer Genome Screening Project utilizing Guardant360, are presented here. Methods Pts with advanced GI tumors who were appropriate for any systemic therapy and had progressed following at least one prior treatment were eligible. We investigated the prevalence of somatic vs. germline BRCA1/2 mutations and the association between BRCA1/2 mutations, TMB and MSI. Results From Jan 2018 to Mar 2019, 850 pts were prospectively enrolled among 26 major cancer centers in Japan. Of 40 (4.7%) actionable BRCA1/2 mutations, 14 were germline: esophagus (squamous cell carcinoma only), 2 pts (N = 62, 3.2%); stomach, 2 pts (N = 131, 1.5%); colorectum, 3 pts (N = 377, 0.8%); pancreas, 3 pts (N = 157, 1.9%); biliary tract, 4 pts (N = 77, 5.2%); and others, none (N = 31, 0%). Notably, the majority of BRCA1/2 mutations (75%) in pts with esophageal, pancreas and biliary tract cancers were germline, while 81% of BRCA1/2 mutations in pts with stomach and colorectal cancers were somatic (p = 0.001). Median TMB of pts with germline BRCA1/2 mutations was significantly lower than those with somatic BRCA1/2 mutations (p = 0.042). In addition, all pts with germline BRCA1/2 mutations were microsatellite stable, while 19% of pts with somatic BRCA1/2 mutations were MSI-high. Conclusions Analysis of cfDNA identified a unique subset of pts with germline BRCA1/2 mutations in advanced GI cancers. Given the association of these findings with efficacy of PARP inhibitor and immune-based therapies, these findings suggest that the identification of BRCA1/2 mutations and their germline-somatic origin may have future implications for therapy selection. Clinical trial identification UMIN000029315. Legal entity responsible for the study SCRUM-Japan GI-SCREEN. Funding Guardant Health, Ono Pharmaceutical. Disclosure Y. Kawamoto: Honoraria (self): Taiho Pharmaceutical Co., Ltd.; Honoraria (self): Daiichi Sankyo Co., Ltd.; Honoraria (self): Takeda Pharmaceutical Co., Ltd.; Honoraria (self): Chugai Pharmaceutical Co., Ltd.; Honoraria (self): Merck Biopharma Co., Ltd.; Honoraria (self): Eli Lilly Japan K.K.. Y. Nakamura: Research grant / Funding (institution): Ono Pharmaceutical; Research grant / Funding (institution): Taiho Pharmaceutical. M. Ikeda: Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Novartis Pharma; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Bayer Yakuhin; Research grant / Funding (institution): Bristol-Myers Squibb; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Eisai; Honoraria (self): Taiho Pharmaceutical; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Eli Lilly Japan; Research grant / Funding (institution): Yakult; Advisory / Consultancy: Otsuka Pharmaceutical; Advisory / Consultancy: Daiichi-Sankyo; Honoraria (self): Sumitomo Dainippon Pharma; Honoraria (self), Advisory / Consultancy: Teijin Pharma; Honoraria (self): EA Pharma; Honoraria (self): MSD; Advisory / Consultancy, Research grant / Funding (institution): ASLAN Pharmaceuticals; Advisory / Consultancy, Research grant / Funding (institution): Chugai Pharmaceutical; Research grant / Funding (institution): Ono Pharmaceutical; Research grant / Funding (institution): AstraZeneca; Research grant / Funding (institution): Merck Serono; Research grant / Funding (institution): Nano Carrier; Honoraria (self): Gilead. H. Bando: Honoraria (self): Taiho Pharmaceutical company; Honoraria (self): Eli Lilly; Research grant / Funding (self): Sysmex; Research grant / Funding (self): AstraZeneca. T. Esaki: Honoraria (self), Research grant / Funding (institution): Taiho; Honoraria (self): Chugai; Honoraria (self), Research grant / Funding (institution): Ono; Honoraria (self): Takeda; Honoraria (self): Bayer; Honoraria (self): Eli Lilly; Research grant / Funding (institution): Astellas; Research grant / Funding (institution): MSD; Research grant / Funding (institution): Daiichi-Sankyo; Research grant / Funding (institution): Merck Serono; Research grant / Funding (institution): Dainippon Sumitomo; Research grant / Funding (institution): Novartis. M. Ueno: Honoraria (self), Research grant / Funding (institution): Taiho Pharmaceutical; Honoraria (self), Research grant / Funding (institution): Yakult Honsha; Honoraria (self), Research grant / Funding (institution): AstraZeneca; Honoraria (self): Novartis; Honoraria (self): Lilly; Honoraria (self): Teijin Pharma; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Shire; Honoraria (self), Research grant / Funding (institution): Ono Pharmaceutical; Honoraria (self), Research grant / Funding (institution): Merck Serono; Research grant / Funding (institution): Daiichi Sankyo; Research grant / Funding (institution): Eisai; Research grant / Funding (institution): MSD; Research grant / Funding (institution): NanoCarrier; Research grant / Funding (institution): Dainippon Sumitomo Pharma; Research grant / Funding (institution): Incyte; Research grant / Funding (institution): ASLAN Pharmaceuticals. T. Nishina: Honoraria (self), Research grant / Funding (institution): Taiho pharmaceutinal; Honoraria (self), Research grant / Funding (institution): Chugai Pharma; Honoraria (self), Research grant / Funding (self): Merck Serono; Honoraria (self), Research grant / Funding (institution): Bristol-Myers Suibb; Honoraria (self): Nihonkayaku; Honoraria (self), Research grant / Funding (institution): Lilly Japan; Honoraria (self), Research grant / Funding (institution): Ono Pharmaceutical; Research grant / Funding (institution): Dainippon Sumitomo Pharma; Research grant / Funding (institution): MSD; Research grant / Funding (institution): Diichi Sankyo. E. Oki: Speaker Bureau / Expert testimony: Taiho Pham; Speaker Bureau / Expert testimony: Yakult Honsha; Speaker Bureau / Expert testimony: Merck; Speaker Bureau / Expert testimony: Chugai Pham; Speaker Bureau / Expert testimony: Takeda Pharm; Speaker Bureau / Expert testimony: Eli Lilly; Speaker Bureau / Expert testimony: Bayer. T. Denda: Speaker Bureau / Expert testimony: DAIICHI SANKYO COMPANY, LIMITED. T. Mizukami: Advisory / Consultancy, Speaker Bureau / Expert testimony, Research grant / Funding (institution): Eli Lilly Japan; Advisory / Consultancy: Bristol-Myers Squibb Company; Speaker Bureau / Expert testimony: Takeda Pharmaceutical; Research grant / Funding (institution): TAIHO Pharmaceutical. N. Okano: Honoraria (self): Taiho Pharmaceutical; Honoraria (self): Merck Serono; Honoraria (self): Eisai; Honoraria (self): Ono Pharmaceutical; Honoraria (self): Yakult Honsha; Honoraria (self): Takeda; Honoraria (self): J-Pharma; Honoraria (self): Kyowa Hakko Kirin. M.I. Lefterova: Shareholder / Stockholder / Stock options, Full / Part-time employment: Guardant Health. J.I. Odegaard: Shareholder / Stockholder / Stock options, Full / Part-time employment: Guardant Health. H. Taniguchi: Honoraria (self): Chugai; Honoraria (self), Research grant / Funding (self): Takeda; Honoraria (self): Taiho; Honoraria (self): Eli Lilly; Research grant / Funding (self): Daiichi-Sankyo; Research grant / Funding (self): Sysmex. C. Morizane: Honoraria (self), Research grant / Funding (institution): Pfizer; Honoraria (self), Advisory / Consultancy: Novartis; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Yakult Honsha; Honoraria (self): Lilly; Honoraria (self), Research grant / Funding (institution): Nobelpharma; Honoraria (self): Fujifilm; Honoraria (self): Teijin Pharma; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Taiho Pharmaceutical; Honoraria (self), Research grant / Funding (institution): Eisai; Advisory / Consultancy: Abbvie; Research grant / Funding (institution): ONO PHARMACEUTICAL; Research grant / Funding (institution): J-Pharma. T. Yoshino: Research grant / Funding (self): Novartis Pharma K.K.; Research grant / Funding (self): MSD.K.K.; Research grant / Funding (self): Sumitomo Dainippon Pharma Co., Ltd.; Research grant / Funding (self): CHUGAI PHARMACEUTICAL Co., Ltd.; Research grant / Funding (self): Sanofi K.K.; Research grant / Funding (self): DAIICHI SANKYO Co., Ltd.; Research grant / Funding (self): PAREXEL International Inc.; Research grant / Funding (self): ONO PHARMACEUTICAL Co., Ltd. All other authors have declared no conflicts of interest.

Background Several studies in BRAFV600E colorectal cancers (CRC) have failed to replicate the efficacy of BRAF inhibitors in treatment of BRAFV600E melanomas (Mel), suggesting the existence of different resistance mechanisms as well as molecular and biological differences between the 2 tumor types. Herein, we examine these differences. Methods Tumor samples submitted to Caris Life Sciences for NGS DNA sequencing (592 gene panel) and RNA sequencing (54 gene panel) between the years 2015 and 2019 were retrospectively studied. Only microsatellite stable (MSS) tumors with either BRAFV600E mutation or wild type (WT) BRAF status were included in this initial analysis. Chi-square tests determined differences. Results A total of 8409 tumor samples were analyzed: CRC (N = 7453: BRAFV600E=373; WT = 7080) and Mel samples (N = 956: BRAFV600E=274; WT = 682). The most frequently mutated genes in BRAFV600E CRC were TP53 (81%), APC (26%), and SMAD4 (22.4%), compared to CDKN2A (22%), PTEN (13%), and TP53 (13%) in BRAFV600E Mel. Molecular alterations that are significantly more frequent in BRAFV600E CRC vs BRAFV600E Mel but not significantly different between BRAF WT CRC vs BRAF WT Mel included RSPO3 fusions (CRC=22.6% vs Mel=0%, P = 0.027); RNF43 deletions (2.0% vs 0%, p = 0.019); and mutations in RNF43 (18.8% vs 0%, P Conclusions BRAFV600E CRC carry molecular alterations that are distinct from BRAFV600E Mel. RSPO3 fusions and RNF43 alterations are prevalent in BRAFV600E CRC tumors in a mutually exclusive manner, suggesting that Wnt pathway activation via genetic alterations in upstream Wnt pathway regulators may play an important role in BRAFV600E CRC tumorigenesis and resistance to BRAF inhibitors. Drug combinations that target both the MAPK and Wnt pathways may warrant further investigation. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure M.E. Salem: Travel / Accommodation / Expenses: Caris Life Sciences. J. Xiu: Full / Part-time employment: Caris Life Sciences. A. Grothey: Travel / Accommodation / Expenses: Caris Life Sciences. R.M. Goldberg: Research grant / Funding (self), Travel / Accommodation / Expenses: Caris Life Sciences. Z. Gatalica: Full / Part-time employment: Caris Life Sciences. R. Feldman: Full / Part-time employment: Caris Life Sciences. M. Saul: Full / Part-time employment: Caris Life Sciences. W..M. Korn: Full / Part-time employment: Caris Life Sciences. A.F. Shields: Research grant / Funding (institution), Travel / Accommodation / Expenses: Caris Life Sciences. J.L. Marshall: Advisory / Consultancy: Caris Life Sciences. H.J. Lenz: Travel / Accommodation / Expenses: Caris Life Sciences. All other authors have declared no conflicts of interest.

e15679Background: The benefits of adjuvant chemotherapy remain controversial in microsatellite stable (MSS) stage II resected colorectal cancer (CRC) patients. In this study, we constructed an over...