Clinical and molecular factors predicting resistance to first-line (1L) FOLFOX in patients (pts) with advanced esophagogastric cancer (EGA) and patterns of subsequent therapy.

Abstract

4047 Background: In the US, FOLFOX is the most widely used 1L treatment for advanced EGA. We evaluated if FOLFOX resistance (FR) impacted subsequent therapy and characterized the clinical and molecular factors that predict resistance to 1L FOLFOX. Methods: We reviewed pts with advanced Her2-negative EGA treated with 1L FOLFOX from Jan 2013 to Aug 2017. Response or stable disease (SD) at time of first restaging scan defined pts as FOLFOX sensitive (FS); progression defined FR. Pt characteristics were compared using Fisher’s exact and Wilcoxon Rank-Sum tests. Outcomes were correlated with clinical variables and MSK-IMPACT data. Microsatellite instable (MSI) pts were excluded from gene and pathway analysis. Overall survival (OS) was calculated from start of FOLFOX using Kaplan-Meier methods. Landmark analysis (2 months [mo] after starting FOLFOX) was used to compare OS between groups. Results: We identified 311 pts, median age 62, 73% male, 82% ECOG 0/1. 246 pts (79%) were FS and 65 (21%) were FR. FR pts had a higher number of metastatic sites, p = 0.001. Median OS was 13.4 mo in FS pts vs 4.3 mo in FR pts (p < 0.001). At time of analysis, 213 pts (172 FS pts and 41 FR pts) and 110 pts (90 FS pts and 20 FR pts) had received 2nd-line (2L) and 3rd-line (3L) chemo respectively. In pts who received 2L chemo (ctx), there was no difference in ctx duration between FS and FR pts (2.1 vs 1.4 mo, p = 0.67). However, in pts who received 3L ctx, the duration was longer in FS vs FR pts (1.6 vs 0.5 months, p = 0.002). In IMPACT tested pts (n = 130), univariate analysis identified EGFR (33.3% vs 10.7%, p = 0.032) and WNT pathway (26.7% vs 4.9%, p = 0.015) alterations more frequently in FR pts vs FS pts. 12 pts were MSI, all were FS (3 SD, 8 PR, 1 CR). Of 63 pts who had IMPACT germline testing, 7 (11%) had germline mutations identified, including CDH1 (n = 2) and ATM (n = 1), all were FS. No pts were enrolled on genotype-matched trials as a result of IMPACT testing. Conclusions: From time of first restaging scan, FR pts have inferior OS to FS pts. The duration of 3L ctx was longer in FS vs FR pts. Higher number of metastatic sites and EGFR and WNT pathway alterations were associated with FR; MSI was not. IMPACT did not facilitate enrolment on genotype-matched studies.