S3834 Unexpected Finding of Metastatic Breast Cancer (MBC) in Diminutive Ascending Colon Polyps

Introduction: Breast cancer, the most prevalent cancer among U.S. women, commonly metastasizes to the lung, bones, and liver. Gastrointestinal (GI) tract involvement is rarely described in the literature. Within the GI tract, colorectal involvement is rare, with the stomach or small intestine being more commonly affected. This is a rare case of metastatic breast cancer incidentally found in a patient with previously treated early-stage breast cancer. Case Description/Methods: A 67-year-old woman with history of stage T1b breast cancer (invasive ductal carcinoma, human epidermal growth factor receptor 2 (HER-2) positive, diagnosed 6 years prior, status post left mastectomy and adjuvant chemotherapy, 5 years in remission) presented for changes in bowel habits, abdominal pain, and bloating. Colonoscopy 9 years prior found a 2 mm hyperplastic polyp, and colonoscopy 14 years prior found a 3 mm tubular adenoma (no dysplasia). Abdominal x-ray showed moderate stool burden and polyethylene glycol daily was initiated. Colonoscopy revealed 6 2 mm sessile polyps, 4 in ascending colon with pathology revealing carcinoma, likely metastasis from a breast primary. Remaining transverse and descending colon polyps were hyperplastic. Computed tomography imaging revealed a lobulated left supraclavicular soft tissue mass and multiple enlarged left iliac chain lymph nodes. Supraclavicular mass biopsy revealed metastatic ductal carcinoma of the breast (HER-2 and estrogen receptor positive). Trastuzumab and pertuzumab were initiated. Discussion: Colonic metastasis from breast cancer is quite rare. Our case demonstrates that endoscopic findings can include small, subtle polyps. This patient, previously in remission, developed metastatic disease diagnosed via pathology of diminutive polyps. This prompted further work up revealing extensive metastatic disease and initiation of treatment. New or nonspecific GI symptoms in breast cancer survivors should prompt a thorough evaluation by GI providers, with consideration of malignancy or disease recurrence as a cause. Though, given subtle endoscopic findings and nonspecific symptoms, it is speculated that the findings in our patient’s case were incidentally found, but with significant impact on her clinical course. Given the expected continued increase in breast cancer survivorship, it is of utmost importance to have a high degree of suspicion and low threshold for sampling on endoscopy, emphasis on adequate bowel preparation and careful colonoscope withdrawal.