Based on the concerns about the actual low strength of evidence of the efficacy of NAC on survival of proper gastric cancer treated with adequate D2 gastrectomy as compared to the results of optimal upfront surgery (S), and considering the actual difficulties of additional RCTs, the aim of this study is to assess the non-inferiority of upfront surgery alone with optimal D2 dissection compared to NAC regimens followed by surgery. Methods: This is a nationwide Multicenter observational retrospective study with matched comparison of two therapeutic strategies (NAC vs S). We will include patients with cT>2, every cN M0, or with every T and N+ M0, histologically proven adenocarcinoma of the stomach, submitted either to pre- or peri-operative treatment and D2 gastrectomy or to upfront D2 gastrectomy, between January 2012 and December 2019, followed by adjuvant treatment when recommended.

All patients matching the inclusion/exclusion criteria will be registered into the study and classified into one of the two arms: a, patients who underwent pre- or perioperative treatment and D2 gastrectomy (NAC) or b, patients submitted to upfront D2 gastrectomy (S). Given the results reported in the "FLOT" trial, a 3-years OS of 55% in the control arm (NAC) was assumed. Three-year OS in the experimental arm (S) was assumed to be 47.4% under the null hypothesis of inferiority and 55% under the alternative hypothesis of non-inferiority. A sample size of 684 patients (342 in each arm) achieves 80% power to detect a non-inferiority margin Hazard Ratio of 1.25

Inclusion Criteria:

• 3.1.1. Locally advanced (T>2 any N or N+ any T) histologically proven adenocarcinoma of the stomach without distant metastases (M0) and without infiltration of adjacent structures and organs.

3.1.2. D2 lymphadenectomy (based on Japanese gastric cancer guideline) 3.1.3. Age > 18 years 3.1.4. surgical resectability 3.1.5. follow-up time of at least 36 months.

Exclusion Criteria:

3.2.1. distant metastases (cM+) or infiltration of adjacent structures or organs (cT4b) and all primarily not resectable stages 3.2.2. Other types of lymphadenectomy lower than D2 3.2.3. Siewert type I and II Cardia cancers 3.2.2. Relapsed gastric cancers 3.2.3. malignant secondary disease, dated back < 5 years (exception: In-situ-carcinoma of the cervix uteri, adequately treated skin basal cell carcinoma)

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4.1.1. This is a nationwide Multicenter observational retrospective study with matched comparison of two therapeutic strategies (NAC vs upfront surgery). Participating centers should have a hospital volume of at least 20 gastric resections for stomach cancer per year. We will include a) patients with cT>2, every cN, or b) patients with every T and N+, histologically proven adenocarcinoma of the stomach without distant metastases (M0) and without involvement of adjacent structures/organs, submitted either to pre- or peri-operative treatment and D2 gastrectomy or to upfront D2 gastrectomy, between January 2012 and December 2019, followed by adjuvant treatment when recommended. All patients who meet the inclusion/exclusion criteria will be registered into the study and classified to one of the two arms based on their treatment (a. Patients who underwent pre- or perioperative treatment and D2 gastrectomy - NAC or b. Patients submitted to upfront D2 gastrectomy- S).