Number of siblings and subsequent gastric cancer risk.

The number of siblings is an indirect indicator of living and, possibly, dietary conditions in childhood and adolescence. The relationship between the number of siblings and subsequent gastric cancer risk was analysed using data from a case--control study conducted in Italy between 1985 and 1992 on 723 cases of incident, histologically confirmed gastric cancer and 2,024 controls in hospital for acute, non-neoplastic, non-digestive tract disorders. After allowance for age and sex, there was a significant trend of increasing gastric cancer risk with increasing number of siblings (P < 0.01). Compared with subjects with no siblings, the relative risk (RR) was 1.1 for those with one, 1.3 for 2, 1.4 for 3-6 and 1.7 for 7 or more siblings. The association was stronger in subjects above the age of 60: the RR for > or = 5 siblings was 1.8, as compared with 1.2 for younger subjects. These patterns of trends are consistent with the hypothesis that domestic crowding and deprivation in childhood and adolescence is a correlate of subsequent gastric cancer risk, and offer therefore interesting clues to our understanding of the process of gastric carcinogenesis.