eP161 - Mets Until Proven Otherwise: Metastatic Breast Cancer 15+ Years Later

Purpose/Background: Metastatic tumors to gastrointestinal (GI) tract are a rare manifestation of cancers originating from skin, ovary, kidney, lungs, hepatobiliary system, stomach, and a very rare manifestation of breast cancer. Lobular carcinoma is the most common breast cancer that metastasizes to GI tract with stomach being the most common site and rarely to colon [1]. The mean interval between primary tumor and metastasis can range from five to thirty years. In this report, we present a case of an incidental finding of multi-focal signet ring cell adenocarcinoma on screening colonoscopy in a patient with a history of breast cancer.Methods/Interventions: A 74-year-old female with a past medical history of diabetes, hypertension, chronic kidney disease, heart failure, atrial fibrillation on oral anticoagulation and breast cancer underwent a screening colonoscopy with an outside provider and was found on biopsy to have a poorly differentiated adenocarcinoma in the proximal transverse colon. She had a mastectomy and axillary lymph node excision in 2007 for lobular breast cancer. She received adjuvant chemoradiation for 1 out of 11 positive lymph nodes. Hormonal therapy (anastrozole) was prescribed for 10 years post-operatively (2017). Colonic biopsy results were followed by metastatic work up including computerized tomography scan of her chest, abdomen, and pelvis that showed no lesion in the colon or anywhere else but a 2.4 cm pancreatic uncinate process cyst. Carcinoembryonic antigen (CEA) test was 9.2 ng/mL.Results/Outcomes: She was to undergo colonoscopy and endoscopic submucosal dissection with possible hemicolectomy. However, repeat colonoscopy revealed masses in ascending, proximal and distal transverse colon. Biopsies were sent and the procedure was aborted. The histopathology was positive for signet ring cell adenocarcinoma, tissue stained negative for MSI-S and HER2. A positron emission tomography scan a week later showed no uptake anywhere in the body.

The tumors were determined to be metastatic lobular estrogen receptor positive breast cancer to the colon and the patient began ribociclib and letrozole treatment after discussion with the gastrointestinal tumor board. The focus of her treatment is on quality of life, rather than curative. Follow-up blood work six weeks after treatment noted her CEA to be 5.4 ng/mL.Conclusion/

Discussion: Metastatic breast cancer to the colon is rare but becoming increasingly more common. The variability in clinical and radiographic appearance makes the timely diagnosis challenging. The treatment of colorectal metastasis can be controversial, but surgery is reserved for complications such as obstruction or symptomatic bleeding.2