Metastatic Breast Cancer to the Cervix and Endometrium Mimicking a Primary Gynecologic Malignancy

The most common sites of breast cancer metastasis include the bone, lung, liver, and brain. Metastasis to the uterine cervix and endometrium is uncommon and can mimic primary gynecologic malignancies, leading to substantial diagnostic challenges. The authors have reported a 56-year-old postmenopausal woman with metastatic invasive mammary carcinoma of the left breast, including biopsy-confirmed liver metastasis, who presented after a syncopal event following an episode of heavy vaginal bleeding. Following her presentation, she underwent cervical and endometrial biopsies. Cervical biopsy revealed scattered discohesive tumor cells positive for GATA3, mammoglobin, TRPS1, AE1/3, and CAM5.2 and negative for PAX8, which were consistent with metastatic breast carcinoma. Endometrial biopsy showed cohesive nests of atypical carcinoma with diffuse p16, p63, and CK5/6 positivity and negative staining for mammoglobin, TRPS1, SOX10, and PAX8, initially raising concern for a human papillomavirus-associated squamous cell carcinoma. Following multidisciplinary evaluation, it was established that these features represented metastatic breast human papillomavirus-associated squamous cell carcinoma to the endometrium rather than a new primary gynecologic malignancy. This case highlighted the importance of considering metastatic disease in patients with breast cancer presenting with abnormal uterine bleeding and demonstrated the value of multidisciplinary evaluation in determining an accurate diagnosis.