Contribution of chemotherapy to improved prognosis in stage 4 gastric cancer: trend analysis of a regional population-based cancer registry in Japan

Little is known about time trends in the prognosis of gastric cancer (GC), since the introduction of new chemotherapeutic agents. This study aimed to analyze how the increased number of available chemotherapeutic options affected the prognosis of GC and which patient types benefited within in a large population. From a population-based cancer registry in Japan, 35,751 cases of GC were identified. Of these, 8214 cases were stage 4. The time trend for 3-year survival in stage 4 GC according to patient characteristics (age and tumor location) was estimated in relation to the introduction of new anticancer drugs. Multiple imputation was performed for sensitivity analysis to strengthen the missing data. In addition, we estimated the 5-year survival rate for distal-GC (DGC) and proximal-GC (PGC), and the hazard ratio (HR) was estimated by Cox proportional hazard model. Improvement of overall survival was accelerated in stage 4 cases over time. The prognosis was improved from 11.4% to 13.2%, subsequent to the approval of several oncologic drugs since 2009. Younger patients were more likely to have improved survival rates in response to the increase in chemotherapy options (< 60-year-old, 5.4%: 60–70, 2.2%; 70–80, 0.3%) from 2007 to 2015. The HR for DGC vs. PGC was 1.11 (95% CI 1.08–1.15), and PGC showed a higher rate of improved outcomes (2.4% vs. 0.6%). This analysis showed that improvement in the GC survival rate was accelerated by the introduction of new chemotherapeutic strategies and it was most evident among younger patients and in patients with PGC.