Risk and survival of third primary cancers in a population-based cohort of gastric cancer patients

Abstract

Background The growing number of gastric cancers together with improved survival resulted in an increasing population of survivors at risk of multiple primary cancers. Aims To estimate the 10-year risk and survival of third primary cancers (TPCs) among gastric first primary cancers (FPCs). Methods Gastric FPCs from the Portuguese North Region Cancer Registry, diagnosed in 2000-2006 (n = 7409), were followed for a TPC (31/12/2012), and for all-cause death (31/12/2017). The cumulative incidence of TPCs was estimated. Patients with a TPC were matched (1:1, by sex, age group, years between FPC and second primary cancer [SPC] diagnosis, and SPC location) to FPC + SPC patients without a TPC. Results Overall, 25 (0.3% of FPCs and 6.8% of SPCs) TPCs were diagnosed. The most common sites were tobacco-related, mainly including digestive organs. Among all FPCs, 10-year cumulative incidence (95% confidence interval [CI]) of a TPC was 0.4% (0.2–0.5%) and among SPCs 7.6% (4.4–10.8%). For TPCs, compared to matched patients, age-adjusted hazard ratio (95%CI) for death was 1.68 (0.77–3.67). The 10-year cumulative mortality of TPCs and matched patients was 92.6% and 67.9%, respectively. Conclusions A clustering of tobacco-related cancers was observed in TPCs, with a 10-year cumulative incidence of 0.4% among FPCs. TPCs had worse survival than patients without a TPC.