Validation of the JCOG prognostic index in advanced gastric cancer using individual patient data from the SPIRITS and G-SOX trials

Abstract

Background: In a phase III study for advanced gastric cancer (AGC), the Japan Clinical Oncology Group (JCOG) 9912 trial, we previously identified the following four prognostic factors—performance status ≥1, number of metastatic sites ≥2, no prior gastrectomy, and abnormal serum alkaline phosphatase levels—and proposed a prognostic index (good risk with 0 or 1 factor, moderate risk with 2 or 3 factors, and poor risk with all 4 factors). To assess the generalizability of this index, we attempted an external validation study using an independent data set. Methods: Individual patient data from the SPIRITS and G-SOX trials were applied to the JCOG prognostic index. The accuracy of the index for predicting survival was assessed by the Cox proportional hazards model. Results: The available data were obtained from 936 (94.5%) of the 990 patients in these trials. The three risk groups categorized by the JCOG prognostic index demonstrated highly significant survival differences; the hazard ratios (95% confidence interval) were 1.71 (1.46–2.01) between the good (n = 338) and moderate (n = 537) risk groups and 3.32 (2.47–4.46) between good and poor (n = 61) risk groups. The median overall survival times of the good, moderate, and poor risk groups were 17.2, 12.0, and 7.8 months, respectively. Conclusions: The JCOG prognostic index was externally validated and can be widely utilized for clinical trials. Further studies are needed to apply this index to the Western population.