Differences in Outcome According to Chemotherapy Backbone and Maintenance Treatment in HER2 Positive Metastatic Gastric Cancer (GC) or Gastroesophageal Junction (GEJ)

Background: Although the TOGA study used cisplatin plus capecitabine (XP) or fluorouracil (FP), oxaliplatin schedules (CAPOX or FOLFOX) are commonly used. There is also a discrepancy in the no. of cycles and the maintenance treatment with trastuzumab (T). Methods: We conducted an observational, retrospective, multicentric study of patients with metastatic HER2 GC or GEJ treated at 6 spanish hospitals belonging to Galician Research Group on Digestive Tumors (GITuD). Demographic, clinic and pathological data were retrospectively collected and correlated with overall survival (OS) and progression free survival (PFS). Results: 91 pts treated between May 2010 to January 2018 were recorded. Median age was 68 years (range 38-84 years), 74.7% were male, 39.6% GEJ location, 82.9% intestinal Lauren subtype, 64.5% well-moderate differentiated, 82.4% synchronous disease and 24.2% primary tumor resection. Median of metastatic locations was 2 (range 1-4). Chemotherapy backbone: FP 4.7%, XP 21.2%, CAPOX 37.6%, FOLFOX 36.5%. With a median follow up of 45.6 months, 85 pts were evaluable for efficacy. Median OS was 14.2 months (CI 95% 10.3-18.0 months) and median first line PFS was 8.9 months (CI 95% 7.7-10.1 months). Overall response rate 57.6% and disease control rate 78.8%. Median cycles of induction treatment were 6 (range 1-18). No PFS differences were found according to the platinum (p = 0.579) or fluropirimidine used (p = 0.955). Of 47 non-progressive patients after 6 months the majority received maintenance treatment for a median of 6.5 cycles (range2-77) with T +/- fluoropirimidine (21 and 16 pts) while 10 discontinued treatment. Post-induction PFS favors those who continued treatment with a PFS of 7.6 vs 5.0 months (p = 0.033), without differences between schemas (p = 0.890)). Primary tumor surgery (HR 0.380; p = 0.010), neutrophil to lymphocyte ratio < 5 (HR 0.461; p = 0.008), platelet to lymphocyte ratio <200 (HR 0.557; p = 0.030) were associated with prolonged OS. Conclusions: Maintenance treatment with T has a benefit in terms of PFS even in patients who received T during induction. The practice of continuing the fluoropirimidine during maintenance doesńt appear to add any PFS benefit in our series. Legal entity responsible for the study: Galician Research Group on Digestive Tumors. Funding: Has not received any funding. Disclosure: All authors have declared no conflicts of interest.