Familial and second gastric carcinomas: a nationwide epidemiologic study from Sweden

BACKGROUND: Familial risks in gastric carcinoma have been assessed mainly through case-control studies based on reported but not medically verified carcinomas in family members. Reliable data on familial risks are needed for prevention and clinical decisions. METHODS: The authors used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and more than 34,000 gastric carcinomas to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for gastric carcinoma in offspring, from birth to 66 years old, by carcinomas in family members. In addition, SIRs for second gastric carcinomas were analyzed. RESULTS: Standardized incidence ratios for gastric carcinoma were 1.31 (95% CI, 0.97-1.70) and 1.47 (95% CI, 1.08-1.92) when a parent presented with gastric carcinoma or gastric adenocarcinoma, respectively. The risk was 1.59 (95% CI, 1.10-2.16) in offspring whose diagnosis was at ages older than 50 years. Offspring risk from parental corpus carcinoma was of borderline significance whereas that from cardia carcinoma was below unity. The sibling risk for gastric carcinoma was 3.16 (95% CI, 1.35-5.72) and 5.75 (95% CI, 2.07-11.26) when diagnosed before age 50. The population attributable proportion of familial gastric carcinoma was 0.45%. Risks for second gastric carcinomas were increased in men and women after esophageal and skin carcinomas, and after non-Hodgkin lymphoma. CONCLUSIONS: The data suggest that environmental factors, perhaps Helicobacter pylori infections are the main reason for familial clustering of gastric carcinoma. The population attributable proportion of familial gastric carcinoma is much lower than that cited in the literature. The patterns of multiple carcinomas suggest that immunologic factors modulate susceptibility to gastric carcinoma.