Development of a staging system and survival prediction model for advanced gastric cancer patients without adjuvant treatment after curative gastrectomy: A retrospective multicenter cohort study

Background: Adjuvant chemotherapy (AC) after curative gastrectomy is the standard treatment for patients with locally advanced gastric adenocarcinoma in East Asia; however, for various reasons, some patients do not receive this treatment. The aim of this study was to develop a system that reflects the survival rate of patients who do not receive AC. Materials and methods: A modified tumor-node-metastasis (TNM) staging system was developed based on the overall survival (OS) of gastric cancer patients after curative gastrectomy without AC at Seoul St. Mary's hospital. A survival prediction model was developed based on the modified staging system and risk factors for OS, which were examined using the Cox proportional hazards regression model. The model was internally validated for the power of prediction and discrimination, compared with the American Joint Committee on Cancer (AJCC) Cancer Staging Manual 8th edition; it was externally validated using data from two other tertiary teaching hospitals. Results: Of the 185 patients in the development set, the 5-year OS rates for modified stages IIA, IIB, IIC, IIIA, and IIIB were 80.2%, 74.0%, 56.7%, 50.0%, and 25.0%, respectively; the median OS intervals for modified stages IIIC and IIID were 21.0 and 11.0 months, respectively. Age, American Society of Anesthesiologists physical status, and postoperative complications were significantly associated with OS. The concordance index (0.768 vs. 0.686), Akaike Information Criterion (745.88 vs. 794.84), and estimated area under the curve (0.7567 vs. 0.6655) were all superior for the prediction model, compared with the AJCC TNM stage. For the validation set of 157 patients, the model performed better for the prediction and discrimination of OS. Conclusion: The newly developed survival prediction model improves the accuracy of OS prediction for stage II and III gastric cancer patients without AC after curative gastrectomy.