Tamoxifen is used as adjuvant therapy for estrogen receptor–positive breast cancer. It has an anti-estrogen effect on the breast but an estrogen effect on the female genital tract. Tamoxifen appears to promote endometrial hyperplasia, polyps, and carcinoma. This risk is more pronounced in women treated for more than 2 years. Should all women taking tamoxifen have serial pelvic ultrasounds or endometrial biopsies to monitor for potential abnormalities? The answer to this question is not clear. Any abnormal bleeding or uterine ultrasound abnormalities in a woman taking tamoxifen should prompt an endometrial biopsy (Barakat, Fornander).