Simple SummaryFLOT-based perioperative chemotherapy is the mainstay of treatment for patients with non-metastatic gastric cancer in Western countries. Although signet-ring cell histology has been proven to be associated with a lack of response to chemotherapy, there is a lack of data concerning whether FLOT-based chemotherapy might be less effective in patients with signet-ring histology. The aim of this retrospective study is to assess whether patients whose gastric cancer is signet-ring cell positive might benefit less compared to others when treated with perioperative FLOT.AbstractBackground: FLOT perioperative chemotherapy represents the standard of care in non-metastatic gastric cancer patients. Signet-ring cell positivity is associated with a worse prognosis in patients with gastric cancer treated with chemotherapy. Comparison between FLOT perioperative chemotherapy vs. surgery followed by adjuvant chemotherapy based on signet-ring cell positivity is lacking. The aim of the analysis was to compare perioperative FLOT with adjuvant chemotherapy in gastric cancer patients stratified by signet-ring cell positivity. Methods: We conducted a retrospective multicenter analysis based on disease-free survival (DFS) and overall survival (OS) in patients with gastric cancer who received perioperative chemotherapy with a FLOT regimen and compared their survival with a historical cohort of patients treated with adjuvant chemotherapy, matched by cT and cN stage and by tumor histological features. Results: Seventy-six patients were enrolled and 24 (32%) were signet-ring cell positive. At a median follow-up time of 39 months, the median DFS was 26.3 months and the median OS was 37.3 months. Signet-ring cell positivity was associated with a shorter OS (median OS: 20.4 vs. 46.9 months, HR: 3.30, 95%CI: 1.56–6.99,p= 0.0018) and DFS (mDFS: 15.2 vs. 38.6 months, HR: 3.18, 95%CI: 1.55–6.54,p= 0.0016). This was confirmed by multivariate analysis for DFS (Exp(B): 2.55) and OS (Exp(B): 2.68). After propensity score matching, statistically significant shorter DFS (HR: 3.30, 95%CI: 1.50–7.35,p= 0.003) and OS (HR: 5.25, 95%CI: 2.18–12–68,p= 0.0002) were observed for patients with signet-ring cell positivity who received perioperative treatment vs. those who received surgery followed by adjuvant chemotherapy. Conclusions: Signet-ring positivity was associated with shorter DFS and OS in patients who received perioperative treatment with FLOT compared with surgery followed by adjuvant therapy. These data suggest that for patients with signet-ring cell histology, FLOT perioperative treatment might not always be the best choice of treatment, and further research should be focused on this group of patients.