Outcomes for advanced HER2-positive gastroesophageal cancer by anatomical location: Experience from the Princess Margaret Cancer Centre

131 Background: The landmark ToGA trial established trastuzumab (T) based therapy as the standard of care for advanced HER2+ gastric and gastroesophageal junction cancer. However, outcomes for T based therapy for HER2+ esophageal cancer have not been well characterized. Methods: We conducted a retrospective analysis of patients (pts) with HER2+ gastroesophageal cancer receiving T based therapy at our institution from 2011-2016. Distal esophagus ( < 35 cm) and Siewert type I/II tumours were defined as esophageal (E). Siewert type III and stomach tumours were defined as gastric (G). Trained abstractors collected pt demographics and treatment details. Overall survival (OS) and progression-free survival (PFS) were calculated from the date of first T treatment. Chi-square tests, t-tests and Cox proportional hazards models were applied where appropriate. Results: We identified 87 pts with advanced HER2+ disease. 62% (n = 54) had de novo metastatic (M1) disease. 57 patients were treated with T based therapy, with median age 57 years (IQR 48-67), 91% baseline performance status 0-1, 19% female, and 7% Asian. 63% (n = 36) had E and 37% (n = 21) had G primary tumours. 67% (n = 38) presented with M1 disease. 33% (n = 19) underwent surgery with curative intent and received T based therapy at recurrence. Baseline characteristics were balanced between the E and G groups. Survival data were available for 51 patients. The E and G groups did not have significant differences in PFS (median 9.5 vs. 9.1 months, HR 0.89 (95% CI 0.44-1.80), p = 0.74) or in OS (median 15.8 vs. 14.2 months, HR 0.88 (95% CI 0.42-1.82), p = 0.73). 63% (n = 36) were treated with subsequent systemic therapy after progression on T, with 23 receiving one line, 9 receiving two lines and 4 receiving three additional lines of treatment. The number subsequent therapies received was similar between E and G groups. Conclusions: Although patients with distal esophagus tumours were not included in the ToGA trial, our analysis suggests that patients with E and G tumours had similar outcomes. Our contemporary cohort had comparable survival outcomes relative to patients receiving T in the ToGA trial (median PFS = 6.7 months, median OS = 13.8 months).