S6337 Polyp Fiction: A Gastric Lesion Reveals a Breast Cancer Story

Introduction: The most common sites of breast cancer metastases include the lungs, liver, brain, and bones. Breast cancer metastases to the stomach are very rare due to blood flow and lymphatic drainage patterns as well as gastrointestinal microenvironmental factors. Case Description/Methods: A 64-year-old woman with history of stage IV ER+ PR+ HER2- invasive lobular carcinoma in remission for nearly 6 years status post right mastectomy and radiation presented to our hospital after a pathologic right femur fracture was discovered. Prior to admission, she had reported severe esophageal reflux symptoms, vomiting, and worsening urinary incontinence to her primary care physician, but did not endorse any changes in bowel habits. She was found to have a new pelvic mass encasing the aorta, inferior vena cava, ureters, lower uterus, and rectum. A computed tomography (CT) scan of her femur showed a pathologic fracture with an associated adjacent ill-defined peripheral enhancing mass predominantly centered within the anterior thigh musculature. Esophagogastroduodenoscopy (EGD) evaluation revealed an 8–10-millimeter gastric polypoid lesion that was biopsied. EUS fine needle aspiration (FNA) of the pelvic mass encasing the rectum was performed. Final pathology results from the femur mass biopsy, gastric polyp biopsy, and rectal mass FNA cytology showed poorly differentiated carcinoma consistent with metastasis from the patient’s primary breast cancer. Discussion: To our knowledge, this is one of the few known cases of incidentally found breast cancer metastases in the gastrointestinal tract after clinical remission that presented with simultaneous gastric and pericolonic involvement. Due to the extremely low rates of breast cancer metastases to the gastrointestinal tract, these types of metastases are often not investigated in routine screening even after the discovery of metastatic breast cancer unless patients demonstrate symptoms concerning for gastrointestinal malignancy. Patients with invasive lobular carcinomas, like our patient, have a stronger incidence of gastrointestinal metastases than ductal carcinomas. As these metastatic lesions can mimic primary gastric malignancy, it is important to obtain definitive pathology results before considering treatment options.