Height, weight, menstrual and reproductive factors and risk of gastric cancer among Japanese postmenopausal women: analysis by subsite and histologic subtype.

To clarify whether reproductive factors have an impact on gastric cancer in Japanese females, a case-control study was conducted using data from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. The study subjects included 365 postmenopausal women with gastric cancer and 1,825 age-class frequency-matched noncancer outpatients presenting at Aichi Cancer Center in 1988-1998. Cases were further divided with regard to the anatomic subsite (upper third, middle third, lower third) and histologic subtypes (differentiated, nondifferentiated) and the association was evaluated using odds ratios (ORs) estimated by the logistic regression model, adjusting for potential confounding factors. A high body weight and corresponding body mass index at age 20 moderately increased the risk of gastric cancer, especially for middle third and nondifferentiated cancers. Risk fluctuation with early or late age at menarche and menopause and total duration of fertility was not consistent. Individuals with a high age at first parity tended to show decreased risk of cancer, irrespective of their subsite or histologic subtype. The ORs were decreased with a short average period of breastfeeding, especially for upper third and nondifferentiated cancers. From these results, however, it appears that height, weight, menstrual and reproductive factors have less impact on gastric cancer than environmental factors such as smoking and dietary habits or family history of gastric cancer.