Tamoxifen, hormone receptors and hormone replacement therapy in women previously treated for breast cancer: a cohort study.

Objective: To determine the risk of recurrence of breast cancer associated with the use of hormone replacement therapy (HRT) in the management of menopausal symptoms in women previously treated for breast cancer who were taking concurrent tamoxifen or who were estrogen receptor-positive.

Methods: The study group comprised 1472 women with histologically confirmed breast cancer, of whom 342 subjects (23.2%) elected to use hormonal therapy in the management of their menopausal symptoms. Women were not excluded from treatment with hormonal therapy if they were taking adjuvant tamoxifen or if they had receptor-positive breast cancer. The response of these patients was compared with that of the rest of the database. A Cox regression analysis was performed with sex hormone usage as time-dependent covariate. Disease-free interval was the outcome measured.

Results: Subjects who took concurrent tamoxifen with combined continuous estrogen-progestogen therapy had a hazard ratio of 0.67 (95% confidence interval (CI) 0.14-3.24, p = 0.62), while concurrent tamoxifen and topical vaginal estrogen users had a hazard ratio of 0.31 (95% CI 0.10-2.57, p = 0.28). The hazard ratio for the estrogen-progestogen users who were estrogen receptor-positive was 0.24 (95% CI 0.10-1.49, p = 0.14).

Conclusions: The use of HRT was not associated with an increased risk of recurrence of breast cancer in women taking concurrent tamoxifen or who were estrogen receptor-positive.