br Material and Methods br The
2. Material and Methods
The eligibility criteria included (1) histologically confirmed gastric adenocarcinoma and R0 resection, which was defined as no macro-scopic and microscopic residual tumor; (2) no other synchronous ma-lignancy; (3) no preoperative chemotherapy or radiotherapy; (4) gas-trectomy and lymphadenectomy based on the Japanese Gastric Cancer treatment guidelines ; (5) more than 14 retrieved Hexa His tag peptide nodes; (6) a postoperative survival time of more than 1 month; and (7) distant metastases patients with pyloric obstruction, stomach bleeding or per-foration who underwent surgery. Lastly, (8) patients with carcinoma of the gastric stump after gastric resection for benign disease were ex-cluded from the study. Between January 2000 and December 2012, 1770 patients underwent surgery at the Department of Gastric & Pan-creatic Surgery, Sun Yat-sen University Cancer Center were included in the current study. Fig. 1 shows the data extraction diagram for our study. The clinicopathological data collected from the database in-cluded gender, tumor size, histological grade, depth of invasion (pT), nodal status (pN), distant metastasis (pM), and the number of retrieved lymph nodes. Pathological staging was according to the 8th [16,17] edition of the AJCC cancer staging manual.
The study was approved by the Research Ethics Committee of Sun Yat-Sen University Cancer Center. Written informed consent was ob-tained from all individual participants included in the study.
The follow-up was done by telephone, email or outpatient depart-ment visits. The last follow-up date was December 2017. The post-operative follow-up included clinical and laboratory examinations every 3 months for the first 2 years at our outpatient department, every 6 months from the third to the fifth years, and annually thereafter until at least 5 years after the operation or until the patient died. The overall patient survival was defined as the time from the operation to death or the last follow-up.
2.3. Statistical analysis
The survival time was calculated from the day of the surgery to the date of death or the last day of follow-up. The 5-year overall survival rate was estimated with the Kaplan-Meier method, and a univariate Surgical Oncology 29 (2019) 90–96
comparison between groups was performed using the log-rank test. In the multivariate analysis, the Cox's proportional hazards model was carried out to calculate the relative risks and to identify the significant prognostic factors. An evaluation of the homogeneity, distinctiveness, and monotonicity was conducted to assess and compare the prognostic ability of the AJCC 8th and m8th staging system. The likelihood ratio χ2 test, related to the Cox regression model, was used to measure homogeneity. The discriminatory ability and monotonicity of the gra-dient assessments were measured with the linear trend χ2 test. The Akaike information criteria (AIC) and Bayesian information criterion (BIC), within a Cox regression model, were also calculated for each system to demonstrate its discriminatory ability. A smaller AIC or BIC value indicated a better optimistic prognostic stratification. All the data analysis was performed by using STATA software (version 14.0, Stata Corporation, Texas, USA). A P value less than 0.05 (two-sided) was considered statistically significant.
3.1. Clinic-pathological characteristics
Of the 1770 patients, 1177 (66.5%) were male, and the mean age was 56.0 ± 12.1 years old. The median number of lymph nodes re-trieved was 26 (range 16–120). The median follow-up was 80 months (range 1–202 months). The overall 5-year survival rate for all the pa-tients was 56.3%, and 1001 patients were alive when our follow-up completed. Seven parameters were significantly associated with the overall survival using the univariate analysis, which were age, tumor size, histological grade, adjuvant chemotherapy status (no matter the drugs or circles), pT, pN and pM (Table 1). In the multivariate analysis, we demonstrated that age, tumor size, histological grade, adjuvant che-motherapy status, pT, pN, and pM stageremained independent prog-nostic factors (Table 1). The details of the population distribution of the AJCC 8th edition staging system is described in Table 2 (except the patients of staging IV, n = 1622).