TITLE:
A Case of Synchronous Advanced Double Cancer of the Breast and Endometrium with Separate Metastatic Pathways, Discovered following Gynecological Surgery
AUTHORS:
Katsutaka Watanabe, Yoshihiko Yonekawa
KEYWORDS:
Breast Cancer, Endometrial Cancer, Synchronous Double Cancer, Invasive Lobular Carcinoma, Metastasis
JOURNAL NAME:
Case Reports in Clinical Medicine,
Vol.14 No.11,
October
29,
2025
ABSTRACT: Synchronous advanced double cancer of the breast and endometrium is an exceptionally rare clinical entity, posing significant diagnostic and therapeutic challenges. We report the case of a 68-year-old woman with endometrioid adenocarcinoma who was incidentally found to have invasive lobular carcinoma of the breast following a modified radical hysterectomy. Intraoperatively, a suspicious lesion on the right adnexa was identified. Histopathological analysis confirmed it to be a metastasis from invasive lobular breast carcinoma, based on its distinct morphology and a specific immunohistochemical profile (CK7+, CK20−, E-cadherin−, Mammaglobin+). Further staging with chest computed tomography revealed multiple pulmonary nodules. A subsequent thoracoscopic lung biopsy was performed to differentiate the primary origin, which was definitively identified as a metastasis from the endometrial cancer. This case is remarkable for the existence of two distinct advanced malignancies with separate distant metastatic sites. Chemotherapy with carboplatin and paclitaxel for the endometrial cancer was initiated but was discontinued after three cycles due to severe adverse events. Subsequently, endocrine therapy with letrozole and palbociclib was commenced for the breast cancer, with the patient maintaining stable disease for over two years. This case highlights the critical importance of definitive histopathological and immunohistochemical analysis to accurately determine the primary origin of metastases in patients with coexisting advanced malignancies, thereby guiding appropriate, individualized treatment.