Synchronous Colonic Adenocarcinoma and Metastatic Lobular Carcinoma in a Colectomy Specimen: A Rare Finding.

Invasive lobular carcinoma is the second-most-common subtype of invasive breast carcinoma. Its metastatic pattern is different compared to invasive carcinoma-no special type. It metastasizes more often to the gastrointestinal tract, peritoneum, pleura, and ovaries. The extrahepatic gastrointestinal tract metastases occur mostly in the stomach and small intestine and less often in the colon and rectum. We present a case description of an 87-year-old woman admitted to our hospital with hematochezia, abdominal discomfort, fatigue, and weight loss. A colonoscopy revealed an exophytic tumor of the sigmoid colon. Metastatic disease was not found in imaging studies. A low anterior resection was performed. The pathologic examination revealed a collision tumor consisting of a poorly differentiated adenocarcinoma of the colon and metastatic lobular carcinoma. The diagnosis was challenging due to the lack of a previous history. Also, the diffuse architectural pattern and signet ring cells found may be in primary signet ring carcinoma of the colon as well as in carcinomas from other anatomical sites. Immunohistochemistry was helpful in making the diagnosis. A review of the literature revealed that this is the fourth case of metastatic breast carcinoma coexisting with colonic adenocarcinoma.