Association of tamoxifen use and ovarian function in patients with invasive or pre-invasive breast cancer

The impact of long-term tamoxifen therapy on ovarian function is not known. Understanding these effects will help reproductive-aged patients who desire future pregnancy make more informed decisions regarding their treatment. This is a retrospective cohort study in patients identified through the UCSF Cancer Registry and SPORE database. We enrolled women with a history of ductal carcinoma in situ (DCIS) or early stage invasive breast cancer who were premenopausal at diagnosis and did not receive chemotherapy. Menstrual histories were obtained through electronic and paper surveys. We compared the age of menopause onset and menstrual pattern changes between women who received tamoxifen (TAM) and those who did not receive tamoxifen (control). Neither group received chemotherapy. 250 subjects were included in this study (125 TAM, 125 control). Mean age of menopause onset was 51.0 for both the groups and was not associated with duration of tamoxifen use or the age at tamoxifen initiation. Menstrual pattern changes, including amenorrhea, were more frequent in the TAM group than control group (any change: 48 % TAM vs. 15 % control, p < 0.001; amenorrhea: 22 % TAM vs. 3 % control, p < 0.001). Older age was associated with an increased risk of developing amenorrhea within 6 months of starting tamoxifen (HR 1.32, p < 0.001). Menstrual pattern changes are common in premenopausal women taking tamoxifen. Tamoxifen use in the absence of chemotherapy is not associated with an earlier age onset of menopause in patients with DCIS or invasive breast cancer and is unlikely to significantly accelerate ovarian aging.