Wu, Christina

685 Background: RAS/BRAF mutations constitutively activate the MAPK pathway in colorectal cancer, and may promote resistance to CRT. We propose that trametinib, a MEK1/2 inhibitor, in combination with 5FU CRT for patients with LARC will improve outcome. Methods: Phase I study with standard 3+3 design in patients with Stage II/III rectal cancer with 3 dose levels of trametinib: 0.5, 1, and 2mg daily with 5FU 225mg/m2/day and 50.4 Gy. Trametinib was given over a 5-day lead-in and continued through the course of CRT. Patients undergo surgery 6-10 weeks after the completion of CRT. An expansion cohort at the maximum tolerated dose (MTD) with 12 patients is ongoing. Tumor tissue is collected prior to therapy, at day 4/5 of trametinib, and at surgery. The primary endpoint is to determine the MTD of trametinib with CRT. Results: 15 patients (10 males, 5 females) have been enrolled and 14 patients are evaluable for toxicities to date. Median age is 53 years (range 35-74). Patients have completed enrollment to all dose levels, with 1 dose-limiting toxicity of diarrhea attributed to 5FU CRT. No grade 4/5 toxicities, and toxicities are shown in the table. Generalized skin rash led to trametinib discontinuation after 2 weeks of therapy for 1 patient, and was held 3 days for 2 patients. At the trametinib dose level of 2mg, 3 out of 7 (43%) patients had a pathological complete response and the average neoadjuvant rectal (NAR) score is 8.1. Tumor RAS/BRAF mutation status is determined. Analysis of tumor tissue shows dose-dependent decrease in phosphorylated-ERK1/2 with increasing doses of trametinib. Conclusions: Initial evaluation shows that the combination of trametinib with 5FU CRT is tolerable and effective, and warrants further investigation in LARC. Clinical trial information: NCT01740648. [Table: see text]

434 Background: Based on the ABC 02 trial, standard therapy for ABTC is CG for up to 8 cycles. However, a recent abstract (Doherty et al, ASCO 2016) confirmed that a cohort of pts does benefit from continued therapy. The weekly administration of G and C can add significant toxicities that may prohibit prolonged treatment (trmt). Previous studies have shown that a biweekly schedule (Ko AH et al JCO 2012) of fixed dose rate (FDR) G helps optimize the prescribed regimen with an improved toxicity profile and added convenience to pts while maintaining efficacy. Methods: Pts with ABTC treated with FDR G (1000mg/m2 at 10mg/m2/min) with C 20mg/m2(GC) on days 1 and 15 of every 28-day cycle were included for analysis. Pts received trmt until time of progression. Data was collected including demographics, clinico-pathologic features, toxicities and survival. Kaplan-Meier curves were used to calculate the median overall survival (OS) and progression free survival (PFS). Results: The study included 109 evaluable pts with ABTC who received CG. Pts had disease that was locally advanced (16.5%) or metastatic (83.5%). Median age was 60 years (28-86). Sites of tumor included gallbladder (21.1%), ampullary (3.6%) and bile duct (75.2%). Median number of cycles was 6 (1-27). Median PFS was 8.34 (6.74, 9.23) months and median OS was 10.32 (9.10, 11.43) months. Most common grade 3 or 4 adverse events included neutropenia (11%), fatigue (10%), thrombocytopenia (TCP) (6.4%), anemia (2.8%), and abnormal liver function tests (2.8%). Fifty-two percent of pts received second line therapy. Conclusions: Biweekly CG in ABTC is associated with a more favorable toxicity profile while maintaining efficacy similar to that observed in prior clinical trials. Minimal toxicities were observed despite a prolonged course for many. Further prospective exploration should consider evaluating the role of biweekly gemcitabine and cisplatin regimen in ABTC especially as a potentially more favorable platform to combine with novel agents. [Table: see text]

BACKGROUNDBiliary tract cancers (BTCs) are uncommon and are associated with a dismal prognosis. Combinations of gemcitabine and platinum chemotherapy (gemcitabine and platinum–based therapy [GP]) form the standard approach for treating advanced BTC. To characterize the spectrum of mutations and to identify potential biomarkers for a GP response in BTC, this study evaluated the genomic landscape and assessed whether mutations affecting DNA repair were associated with GP resistance.METHODSPretreatment, formalin‐fixed, paraffin‐embedded samples from 183 BTC patients treated with GP were analyzed. Cox regression models were used to determine the association between mutations, progression‐free survival (PFS), and overall survival (OS).RESULTSWhen genes with an incidence > 10% were considered, no individual gene was independently predictive of a GP response. In patients with unresectable BTC who received GP as their first‐line therapy, the joint status of cyclin‐dependent kinase inhibitor 2A (CDKN2A), tumor protein 53 (TP53), and AT‐rich interaction domain 1A (ARID1A) was associated with PFS (P = .0004) and OS (P ≤ .0001). Patients with mutations in CDKN2A and TP53 were identified as a poor‐prognosis cohort with a median PFS of 2.63 months and a median OS of 5.22 months. Patients with mutant ARID1A, regardless of the single‐mutation status of TP53 or CDKN2A, had similar outcomes. A patient who exhibited mutations in all 3 genes had a median PFS of 20.37 months, and OS was not reached.CONCLUSIONSIn the largest exploratory analysis of this kind for BTC, 3 prevalent, mutually exclusive mutations represent distinct patient cohorts. These mutations are prognostic and may represent a predictive biomarker for a GP response. Prospective studies to validate these findings are needed, and they should include the incorporation of therapies that exploit the genomic instability observed with these mutations in BTC. Cancer 2016;122:3657‐66. © 2016 American Cancer Society.