Hormone exposure and estrogen receptor status at breast cancer diagnosis: Implications on survival

To examine if hormone exposures including oral contraceptive use, pregnancy, breast feeding, and estrogen replacement therapy (ERT) were associated with estrogen receptor (ER) status at breast cancer diagnosis and all-cause and breast cancer-specific mortality, we studied population-based incident breast cancer cases, excluding women with previous cancer diagnosis, in situ cases and cases without recorded ER status. The sample of 582 women provided information on hormonal exposures prior to diagnosis in 1994-1995, including pregnancy, breast feeding, oral contraceptive and ERT use. Survival analyses using Cox proportional hazards regression were used to examine the role of hormonal exposures on all-cause and breast cancer-specific mortality, using cancer registry data through 2004. History of pregnancy was associated with ER+ status at diagnosis in pre-menopausal women (OR=2.32; 95%CI: 1.05, 5.11). Among post-menopausal women, history of ERT use was associated with ER+ status (OR=2.01; 95% CI: 1.13, 3.56). Multivariate survival analyses indicated that ERT use in ER+ post-menopausal women improved all-cause and breast cancer-specific mortality (HR=0.45; 95% CI: 0.28, 0.68). We conclude that different hormonal exposures are associated with ER+ status at diagnosis between pre- and post-menopausal women, but the specific mechanisms remain unknown. ERT use before breast cancer diagnosis in ER+ post-menopausal women was observed to promote survival, perhaps due to removal upon diagnosis of hormonal “fuel” for tumor growth in women with hormone-sensitive breast cancer.