Late Gastrointestinal and Genitourinary Progression of Metastatic Invasive Lobular Breast Carcinoma: A Case Report

Gastrointestinal (GI) and genitourinary (GU) metastases from breast cancer are uncommon and are most frequently associated with invasive lobular carcinoma (ILC). These metastases may occur many years after initial diagnosis and can closely mimic primary colorectal or urothelial malignancies, posing significant diagnostic challenges. We report the case of a 64-year-old woman with hormone receptor–positive, HER2-negative bilateral ILC diagnosed in 2010 and treated with neoadjuvant chemotherapy, bilateral mastectomy, radiation, and prolonged endocrine therapy. Microscopic ovarian involvement identified at prophylactic bilateral salpingo-oophorectomy in 2011 established stage IV disease, followed years later by biopsy-confirmed adrenal metastasis treated with radiation and systemic therapy. More than a decade after initial diagnosis and in the setting of established metastatic disease, surveillance imaging identified lesions in the sigmoid colon and left urinary bladder wall. Biopsies from both sites demonstrated metastatic ILC on histomorphology and immunohistochemical (IHC) profiling, supporting metastatic rather than new primary malignancy. The bladder wall lesion demonstrated minimal metabolic activity on PET/CT despite histologic confirmation, highlighting the limited sensitivity of functional imaging in ILC. The patient was treated with fulvestrant and everolimus, with subsequent radiographic stability and decline in tumor markers CA 15-3 and CA 27.29; these findings represent an individual clinical course rather than evidence of treatment efficacy. This case underscores the importance of maintaining diagnostic vigilance for late GI and GU metastases with ILC. It highlights the role of tissue diagnosis and panel-based IHC interpretation in guiding management.