| Objectives. To evaluate the relationship between hormonal/reproductive factors and gastric cancer (GC) by anatomical subsite (proximal and distal stomach) and histological subtype (diffuse and intestinal).; Methods. Data was analysed from a population-based case-control study conducted in eight Canadian provinces. Cases comprised 326 women and 711 men ages 20–74 years with incident, pathology confirmed GC; all cases were subclassified by anatomical and histological subgroups. Controls were 326 women and 711 men, 1:1 frequency-matched to the cases on age. Hormonal/reproductive factors were studied only in the women. Information on exposure and other risk factors for disease was captured through self-administered questionnaire. Risk estimates were generated by multiple logistic regression and age-adjusted odds ratios were calculated for anatomical/histological subgroups.; Results. After adjusting for possible confounders, later age at menarche was associated with an increased risk of GC compared with onset of menarche less than 13 years of age (13–14 years: OR = 1.45, 95% confidence interval (CI): 1.00–2.10, ≥15 years: OR = 1.93, 95%CI: 1.19–3.13). Compared to premenopause, natural menopause was associated with an increased risk of GC (OR = 1.99, 95% CI: 0.98–4.05). Being pregnant for 5 months or more was associated with a nonsignificant decreased risk of GC relative to nulliparity (<24 years of age OR = 0.55, 95%CI: 0.31–0.99; ≥25 years of age OR = 0.69, 95% CI: 0.39–1.25), as was having 4 or more births (OR = 0.56, 95%CI: 0.32–0.99). No association was observed with use of oral contraceptives, use of hormone replacement therapy, bilateral oophorectomy or years of fertility. Early age at menopause was associated with an increased risk of intestinal adenocarcinoma and use of oral contraceptives was associated with a decreased risk of intestinal type. Many associations were more pronounced in proximal GC compared to distal, and intestinal type histology compared to diffuse.; Conclusions. Hormonal/reproductive factors associated with a greater exposure to estrogen and/or progesterone (early age at menarche, late age at menopause, parity, exogenous hormone use) were associated with a decreased risk of GC. Moreover, these associations were more pronounced in male predominant GC subtypes (proximal GC and intestinal type adenocarcinoma). These findings may explain, in part, why females are at a decreased risk of GC than males. |
