Since 2006, surgery combined with perioperative chemotherapy is the standard of care for resectable gastric adenocarcinoma in Europe. Specific effects of neoadjuvant chemotherapy remain unknown. The aim was to evaluate the rate of tumor downstaging and its impact on survival in patients undergoing curative resection after neoadjuvant chemotherapy (NeoCT) for gastric adenocarcinoma.
All patients treated in a curative intent for gastric or esophagogastric junction adenocarcinomas between 1996 and 2016 in our high-volume center were retrospectively included. Tumor downstaging after NeoCT was defined as ypTN inferior to cTN. The accuracy of clinical staging was evaluated in patients treated by upfront surgery before 2006.
During the study period, 491 patients were operated for gastric adenocarcinoma, and 449 patients were finally analyzed. Among the 163 (36.3%) patients who received NeoCT, 61 (37.4%) had tumor downstaging. Overall survival and disease-free survival were longer in patients with tumor downstaging compared to patients without it (5-year survival: 84.8% vs 49.7%; P = .002 and 61.7% vs 43.4%; P = .054). In multivariate analysis tumor downstaging was an independent prognosis factor for better overall survival (HR = 5.258; P = .002) and disease-free survival (HR = 2.286; P = .028). Moreover, 45.5% of patients staged cT1-T2N0, in whom upfront surgery was performed, were understaged and ultimately had a more advanced tumor on pathological analysis.
Response to neoadjuvant chemotherapy constitutes a major prognostic factor for overall and disease-free survival. In the absence of predictive factors for tumor downstaging, the indication for perioperative chemotherapy should remain broad, in particular because of the low accuracy of pretherapeutic staging and therefore the high risk of understaging tumors.

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