Tamoxifen in the Management of Breast Cancer: A Case Presented in Multidisciplinary Session With Clinical Discussion and Decision-Making

Selective estrogen receptor modulators (SERMs) have been shown to reduce the risk of developing estrogen-positive breast cancer. Tamoxifen, a potent SERM, has been successfully administered as adjuvant therapy for breast cancer. However, uterine pathologic changes may develop due to the effect of tamoxifen as both an agonist and antagonist of estrogen on the uterus. Here, we discuss a case of breast cancer treated with tamoxifen to clarify one of the most important complications, namely, endometrial hyperplasia. A 51-year-old woman presented with left breast mass and axillary lymphadenopathy. Mammography showed a 26-mm spiculated mass consistent with invasive ductal carcinoma in core needle biopsy. Immunohistochemical analysis revealed that the tumor was ER- and PR-positive, HER2-negative, and P53-negative. Adjuvant chemotherapy was completed, and the patient was referred to undergo adjuvant radiotherapy (RT). After the completion of RT, treatment with tamoxifen was initiated at the recommended dose of 20 mg/day. The questions are when to use tamoxifen as adjuvant therapy for breast cancer, How to follow the patient treated with tamoxifen, and when to discontinue tamoxifen therapy. Use of tamoxifen for at least 5 years after diagnosis is a reasonable option for the prevention of breast cancer or its recurrence in high-risk patients. Premenopausal women on tamoxifen presenting with abnormal uterine bleeding must undergo transvaginal ultrasonography. For premenopausal women taking tamoxifen, irregular vaginal bleeding should be evaluated by hysteroscopy or uterine ultrasonography, and, if the etiology remains unclear, a biopsy should be done. There are no evidence-based recommendations for uterine malignancy screening in patients who take tamoxifen. Current recommendations are annual gynecologic examination and evaluation of any abnormal vaginal bleeding.