Reproductive and sex hormonal factors and oesophageal and gastric junction adenocarcinoma: a pooled analysis.

BACKGROUND The rapidly rising incidence and the striking male predominance are as yet unexplained features of oesophageal and gastric junction adenocarcinoma. Few and underpowered studies have examined the impact of female reproductive factors on risk of these adenocarcinomas in women. We therefore pooled data on women from four population-based case-control studies to examine the association of female reproductive and sex hormonal factors with oesophageal and gastric junction adenocarcinoma. METHODS Data on women from case-control studies conducted in Ireland, the United Kingdom (UK), Australia and United States of America (USA) were pooled. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for a range of reproductive factors, adjusted for age, study and major risk factors for oesophageal and gastric junction adenocarcinoma. RESULTS We included 218 cases and 862 controls. Among parous women, a reduced risk of oesophageal and gastric junction adenocarcinoma was found after breastfeeding (OR=0.58, 95% CI=0.37-0.92) and the risk decreased with increased duration of breastfeeding (>12 months OR=0.42, 95% CI=0.23-0.77). The endogenous reproductive factors such as parity, menstruation, history of pregnancy and the exogenous factors such as use of oral contraceptives and of hormone replacement therapy were not statistically significantly associated with oesophageal and gastric junction adenocarcinoma. CONCLUSION Our findings suggest that breastfeeding is associated with a decreased risk of oesophageal and gastric junction adenocarcinoma. The potential mechanism of this association warrants further investigation.