Pattern of recurrence and overall survival in esophagogastric cancer after perioperative FLOT and Clinical Outcomes in MSI-H population: The PROSECCO Study.

Abstract

e16068 Background: The FLOT4-AIO phase II/III trial established perioperative FLOT regimen as the new standard in Western countries for patients (pts) with locally advanced resectable gastric (GC) or gastroesophageal junction cancer (GEJC). Microsatellite instability (MSI-H) showed a favorable prognostic role and a concomitant negative predictive impact on the benefit of adjuvant and neoadjuvant 5-fluorouracil-based doublets, but its prognostic and predictive role in pts receiving perioperative FLOT treatment still remains unclear. Our study aims to explore the real-world efficacy of FLOT regimen and to describe histopathological features and clinical outcomes in the MSI-H subgroup population. Methods: This is a retrospective multi-center analysis including pts with GC and GEJC, treated with perioperative FLOT regimen in clinical practice and whose microsatellite status and survival data were available. The association of baseline characteristics, biomolecular and pathological features and overall survival (OS) were firstly assessed in univariate analyses by means of log-rank test, and significantly prognostic variables (p < .05) were included in a multivariable COX proportional hazard model. Results: A total of 250 pts (median age, 62, range 37-81, male 71.6%, ECOG PS 0, 82%) were treated at 11 Italian Oncology Units from January 2017 to June 2021. At a median follow-up time of 22.5 months (mos) (2.3 - 66.7 mos), 123/250 (49.2%) patients relapsed and 77/250 (30.8 %) died. In the global population the median disease-free survival (DFS) was 16,7 mos (95% CI 13,8–21,2) and the median OS 34,9 mos [95% confidence interval (CI) 28–NA]. MSI-H phenotype was found in 26 (10.4%) out of 250 analyzed tumors. Compared to MSS cases, MSI-H were more frequently identified in female (50% vs 25.9%, p = .001), elderly pts (age ≥ 70 years, 76.9% vs 9.4%, p = .003), Laurens’s intestinal type (54% vs 12%, p = .0076) and in pts with primary location tumor in antrum (38.5% vs 13.8%, p = .0004). No relevant differences have been noticed in R0 resections (88% and 96%, p = .06) and pathological complete responses (4.9 % and 3.8%, p = .718), however a statistically significant difference in the rate of pathological negative lymph-nodes between MSS and MSI-H cohort emerged (29.3% vs 65.4%, p = .0004). Compared to MSS tumor population, MSI-H subgroup has a tendency to better DFS (median not reached (NR) vs 15.7, p = .06), metastasis free survival (MFS, median NR vs 17.2 mos, p = .06) and OS (median 41 vs 34 mos, p = .07). Conclusions: These real-world data confirm the efficacy of FLOT perioperative regimen in pts with locally advanced GC/GEJC, maintained also in the MSI-H pts. Our study suggests a better outcome of MSI-H GC and GECJ pts treated with FLOT in comparison to MSS, due to increased rate of nodal status downstaging and despite a poor histological response in the resected tumor tissue of MSI-H pts.