Colonic Metastasis of Previously Undetected Invasive Lobular Carcinoma in a 68-Year-Old Woman Undergoing Regular Breast Screening.

Invasive lobular carcinoma (ILC) is a breast cancer subtype known for its subtle presentation and potential for unusual metastatic spread. We present the case of a 68-year-old woman with vague abdominal pain and a positive fecal occult blood test. Colonoscopy revealed a vegetative neoplasm in the cecum with ileocecal valve stenosis. Initial histopathology, performed during endoscopy, identified an epithelial infiltrative histotype but did not allow further characterization due to limited differentiation. The tumor was staged with a contrast-enhanced thoracoabdominal CT scan, and multidisciplinary discussion led to a videolaparoscopic right hemicolectomy. Final histopathology revealed extensive infiltration consistent with ILC, luminal A subtype. Although the patient reported regular breast cancer screening with annual mammography and ultrasound, no abnormalities had been previously detected. Postoperative imaging confirmed a retroareolar breast lesion with nipple retraction and axillary lymphadenopathy. Following multidisciplinary discussion at the Breast Unit, further histologic typing was deemed unnecessary, and the patient was started on endocrine therapy combined with a CDK4/6 inhibitor. This case highlights a rare presentation of ILC and underscores the importance of maintaining clinical suspicion for metastatic breast cancer in patients with gastrointestinal lesions and inconclusive endoscopic findings.