Predictors of resistance to trastuzumab deruxtecan (T-DXd) in esophagogastric adenocarcinoma (EGC).

Abstract

e16024 Background: In DESTINY-Gastric01/02, T-DXd improved objective response rates (ORR) and overall survival (OS) relative to chemotherapy in patients (pts) with trastuzumab-refractory HER2+ EGC. We sought to identify clinicopathologic features that predict response and resistance to T-DXd, in a cohort from Memorial Sloan Kettering Cancer Center (MSKCC). Methods: Demographics of pts with HER2+ (HER2 IHC 3+ or IHC 2+/FISH+) advanced EGC at MSKCC treated with T-DXd in 2nd line or later (2L+) from 2017 to 2022 were reviewed via the medical record. Progression-free survival (PFS) and OS were calculated from T-DXd initiation to event or last follow up. Univariate (UV) and multivariable (MV) analyses of PFS were performed using Cox proportional hazards models. Categorical comparisons used the χ2 or Fisher’s exact test when subgroup n < 5. Results: 57 pts received 2L+ T-DXd (25 2L, 18 3L, 14 4L+). Median age at treatment was 64.5 years and most pts were male (74%) and white (82%) with primary tumors in the esophagus/GE junction (72%) and HER2 IHC 3+ expression (82%). With median follow up of 12 months (mos), ORR was 49% with median PFS (mPFS) of 5.4 mos (95% CI 3.2 – 6.8) and median OS (mOS) of 13 mos (95% CI 8.5 – 19). Pts with HER2 IHC 2+ EGC had lower ORR (30% vs 53%, p = 0.3) and inferior PFS compared to IHC 3+ in UV analysis (HR 2.58, 95% CI 1.08 – 6.13 mos, p = 0.03). Pts with HER2 retesting (n = 22) within 1 mo prior to T-DXd had higher ORR (64% vs 40%, p = 0.08); HER2 IHC in 4 of these pts decreased from 3+ to 2+. Despite irinotecan (irino) ORR of 38% prior to T-DXd in 8 pts, only 1 (12%) had OR to T-DXd. Furthermore, only one of the 12 pts (8%) who received irino following T-DXd had OR to irino, despite T-DXd ORR of 42% among these pts. Irino-treated pts also had worse PFS on T-DXd (vs no prior irino, HR 4.91, 95% CI 2.09 – 11.5 mos, p < 0.001). Prior checkpoint inhibition was not associated with PFS on T-DXd. In MV analysis, prior irino therapy remained significantly associated with progression/death (HR 4.12, 95% CI 1.63 – 10.4 mos, p = 0.003), and not HER2 IHC 2+ (vs 3+) nor 3L+ treatment (vs 2L). Additional correlations with genomic alterations will be presented. Conclusions: Consistent with DESTINY-Gastric trials, approximately half of pts with EGC at MSKCC had OR to T-DXd with mOS > 1 year. However, our real-world findings suggesting lower ORR in patients with sequential T-DXd and irinotecan-containing therapy and those without pre-T-DXd HER2 IHC confirmation merit further validation in future studies.