Objective To investigate the impact of postoperative adjuvant chemotherapy on the prognosis of patients undergoing radical gastrectomy for gastric cancer.

Methods The propensity score matching (PSM) and retrospective cohort study was conducted. The clinicopathological data of 6 135 patients who underwent radical gastrectomy for gastric cancer at Zhejiang Cancer Hospital from January 2007 to December 2019 were collected. There were 4 376 males and 1 759 females, aged 61 (range, 19-92) years. Among the 6 135 patients, 3 530 cases who did not receive postoperative adjuvant therapy were assigned to the NAC group, and 2 605 patients who received postoperative adjuvant therapy were assigned to the AC group. Observation indicators: (1) propensity score matching and comparison of clinicopathological characteristics of patients after matching; (2) follow‑up; (3) analysis of prognostic factors of patients; (4) prognosis of patients with different age. Comparison of count data between groups was conducted using the chi‑square test. Comparison of ordinal data was conducted using the non‑parametric rank‑sum test. Univariate and multivariate analyses were performed using the Cox proportional hazard model. The Kaplan‑Meier method was used to calculate survival rates and draw survival curves. The Log‑rank test was used for survival analysis. PSM was done by the 1∶1 nearest neighbor matching method, with a caliper of 0.02.

Results (1) Propensity score matching and comparison of clinicopathological characteristics after matching: among the 6 135 patients, 3 642 cases were successfully matched, with 1 821 cases in each group. After PSM, potential confounding biases including age, family history, surgical approach, extent of gastrectomy, tumor location, pathological type, differentiation degree, vascular invasion, neural invasion, recurrence/metastasis, pathological TNM stage, pathological T stage, and pathological N stage were eliminated, ensuring comparability between the two groups. (2) Follow‑up: after PSM, all patients were followed up postoperatively for 60 (range, 0-180) months. During follow‑up, 894 deaths occurred in the non‑AC group and 673 deaths occurred in the AC group. The 3‑, 5‑year overall survival rates were 56.3% and 46.0% in the non‑AC group, versus 69.5% and 61.2% in the AC group, respectively, showing a significant difference of overall survival between the two groups (χ²=74.45, P<0.05). (3) Analysis of prognostic factors of patients: results of multivariate analysis after PSM showed that gender, age (middle age versus youth), age (old age versus youth), adjuvant chemotherapy, surgical approach, extent of gastrectomy (proximal gastrectomy versus distal gastrectomy), tumor location (≥2 locations versus 1/3 of the upper part of stomach), pathological type, vascular and neural invasion, recurrence and metastasis, pathological T stage (T3 stage versus T1 stage), pathological T stage (T4 stage versus T1 stage), and pathological N stage (N1 stage versus N0 stage), pathological N stage (N2 stage versus N0 stage), pathological N stage (N3 stage versus N0 stage) were independent prognostic factors for patients undergoing radical gastrectomy for gastric cancer (hazard ratio=0.88, 1.40, 2.14, 0.63, 1.22, 0.66, 1.28, 1.26, 1.22, 1.22, 1.82, 2.41, 3.30, 1.50, 2.11, 4.10, 95% confidence interval as 0.79-0.99, 1.03-1.89, 1.59-2.86, 0.57-0.69, 1.03-1.46, 0.50-0.87, 1.10-1.50, 1.09-1.45, 1.09-1.37, 1.08-1.38, 1.51-2.19, 1.51-3.86, 2.07-5.27, 1.10-2.05, 1.51-2.94, 2.92-5.75, P<0.05). (4) Prognosis of patients with different age: after PSM, in 1 091 middle aged patients, the 3‑year overall survival rates were 81.4% for 531 patients with postoperative adjuvant chemotherapy versus 71.7% for 560 patients without postoperative adjuvant chemotherapy, the 5‑year overall survival rates were 76.2% versus 65.4%, showing significant differences between them (χ²=11.63, P<0.05). In 2 313 old age patients, the 3‑year overall survival rates were 69.5% for 1 181 pati-ents with postoperative adjuvant chemotherapy versus 56.3% for 1 132 patients without postoperative adjuvant chemotherapy, the 5‑year overall survival rates were 61.2% versus 46.0%, showing significant differences between them (χ²=64.93, P<0.05).

Conclusion Postoperative adjuvant chemo-therapy provides a survival benefit for patients undergoing radical gastrectomy, particularly for middle aged and old age patients, significantly improving overall survival rates. Gender, age, adjuvant chemotherapy, surgical approach, extent of gastrectomy, tumor location, pathological type, vascular and neural invasion, recurrence and metastasis, pathological T stage, and pathological N stage are independent prognostic factors for patients undergoing radical gastrectomy for gastric cancer.