Table 1 summarizes the main clinical and pathological features of the studied populations. The median age was 72 years old and the Male/Female (M/F) ratio was 1.6. The median follow-up was 85 months. The entire studied population was divided into two groups “Upfront” and “NAC.” In particular, 206 patients were categorized in the “Upfront” cohort and 50 patients in the “NAC” one.

The 5- and 10-y OS of the entire population were 59.2% and 56.4%, respectively (Supplementary Fig. 1). Instead, the 5- and 10-y DFS were 57% (supplementary Fig. 2). Figure 1 shows the 5–10-year OS of patients stratified according to the presence of POC, distinguished, respectively, in POC and nPOC (without post-operative complications) within the above mentioned two cohorts, “Upfront” and “NAC.” In the first cohort, the 5- and 10-year OS were 59.1% in the nPOC group and 52.1% and 47.9% in the POC group, respectively. The survival of the nPOC group was better than the POC group, but no statistically significant difference was found (p = 0.14).

Overall Survival in upfront cohort (a) and NAC cohort (b)

We observed the same in the “NAC” cohort, where the 5- and 10-year OS were even better in POC group than in the nPOC group, 81% vs. 79.7% and 81% vs. 71.8%, respectively (p = 0.81).

Figure 2 describes the DFS of nPOC and POC groups in the two cohorts of patients. In "Upfront” cohort, the 5- and 10-y DFS were 52.8% in the nPOC group and 53.9% in the POC group. No statistically significant difference was found (p = 0.93). In the “NAC” cohort, patients without POC had a DFS close to that of patients with POC (74.6% vs. 73.4%, respectively; p = 0.77).

Disease Free Survival in upfront cohort (a) and NAC cohort (b)

Finally, we only considered the POC group, dichotomizing patients in upfront and NAC. Comparing clinical and pathological features of the two subgroups of patients with POC, we showed no difference in sex, histological type, lymph node dissection, ypT, ypN, ypM, and pathological stage. Instead, the tumor location, the type of gastrectomy, and the grade of POC were different between the two groups (p = 0.009, p = 0.029, and p = 0.037, respectively) as well as are described in Table 2. After that, we analyzed survival and we showed a statistically significant difference in OS between patients with POC who underwent surgery at first or NAC before surgery (p = 0.04, HR 3.236, 95% CI 1.569–6.675) (Fig. 3). The first group had a 5- and 10-year OS of 52.1% and 47.9%, whereas the latter group had a 5- and 10-y OS of 81%. Considering DFS, we did not find a statistically significant difference between the two cohorts. In fact, the 5- and 10-year DFS of patients underwent surgery at first were both 53.9% and the 5- and 10-y DFS of patients underwent NAC were both 73.4% (p = 0.135; HR 2.110, 95% CI 0.974–4.565). Moreover, we found a statistically significant difference in OS in the POC group considering age (p = 0.02), NAC (p = 0.02), pT (p = 0.0005), pN (p < 0.0001), pM (p = 0.008), pStage (p < 0.0001), lymphovascular invasion (LVI) (p = 0.0008), and perineurial invasion (PNI) (p = 0.002). In multivariate analysis, age and NAC were identified as independent prognostic factors for OS (p = 0.0071 and p = 0.0098, respectively).

Overall Survival in patients with postoperative complications in the two cohorts

The severity and type of POC are summarized in Table 3. No grade V has been included in this study. Among the 256 patients, grade I, II, III, and IV complications were observed in 26 (10.2%), 90 (35.2%), 12 (4.7%), and 10 (3.9%) patients, respectively.

Analyzing the different grades of POC, we showed a higher number of grade I and II POC than grade III and IV (116 vs. 22, respectively). In addition, considering only grade II, we showed that the major cause of complications was anemia requiring transfusion.

Considering the “Upfront” cohort, we did not find a statistically significant difference in OS according to grades I–II and grades III–IV; in particular, patients with grade I–II had a 5- and 10-year OS of 54.1% and 49.6%, whereas the 5-year OS of patients with grades III–IV was 39.3% (p = 0.20). In the “NAC” group we did not find a statistically significant difference in 5-y OS (83.3% vs. 80.7%; p = 0.91). No significant statistically difference was found in DFS.