Background: Tamoxifen has been successfully administered as adjunctive therapy for breast cancer. However, the effect of tamoxifen as an estrogen agonist and antagonist can cause pathological changes in the uterus. The agonist effect may stimulate endometrial proliferation leading to endometrial polyps, hyperplasia, and, rarely, endometrial cancer. Objective: We present the case of tamoxifen-treated breast cancer case to better understand one of the most serious consequences, endometrial cancer. Case presentation: A 37-year-old woman came to our centre with complaints of abnormal vaginal bleeding. She has diagnosed with grade I infiltrative ductal carcinoma in 2018, with primary complaints of right breast mass and axillary lymphadenopathy. During this period, adjuvant chemotherapy was given tamoxifen 20 mg once daily. There were no complaints or relapses at a six-month follow-up over three years. In the fourth year, the patient complained of vaginal bleeding. A vaginal biopsy was performed, and the results showed low-grade endometrioid-type endometrial carcinoma. Total hysterectomy and bilateral salpingo-oophorectomy were performed with the resultant mass of up to half of the myometrial lining with metastatic negative parallax lymph nodes. Conclusion: Following tamoxifen therapy, endometrial cancer is more likely to occur in patients. Patients who experience irregular vaginal hemorrhage should have hysteroscopy or uterine ultrasound performed, and if the cause is unknown, a biopsy should be performed.
Key words: endometrial cancer, tamoxifen, premenopausal, cancer treatment.
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