Endometrial Carcinoma Unveiling Breast Carcinoma in a Postmenopausal Female: A Case of Synchronous Malignancy.

Background: The ability to detect multiple primary malignancies in a single patient has improved because of modern cancer screening and imaging technologies. While both endometrial and breast carcinomas are common in postmenopausal women, concomitant presentation is uncommon. Case Report: A 61-year-old postmenopausal female initially presented with abdominal pain and postmenopausal bleeding. Positron emission tomography/computed tomography revealed fluorodeoxyglucose-avid lesions in the left breast and axilla, although mammography showed Breast Imaging Reporting and Data System category 1. Clinical breast and axillary examinations were unremarkable. Immunohistochemistry demonstrated GATA binding protein 3 and human epidermal growth factor receptor 2 positivity in the axillary lymph nodes, suggestive of breast carcinoma, while positivity for paired box gene 8, estrogen receptors, and progesterone receptors supported an endometrial tumor. Genetic testing panel results were negative. After undergoing neoadjuvant chemotherapy, the patient had marked regression in the endometrial lesion and a pathologic complete response in the breast lesion. Conclusion: Because of the infrequency and clinical complexity associated with synchronous malignancies, this case highlights the importance of a multidisciplinary approach, advanced imaging, and molecular profiling for accurate diagnosis and personalized treatment planning.