A Gastric Metastatic Lesion That Resembled Early-Stage Gastric Cancer on Endoscopy during Treatment for Recurrent Breast Cancer: A Case Report

Breast cancer metastasis to the gastrointestinal tract is relatively rare. Patients with such disease often develop gastrointestinal symptoms, but it is sometimes asymptomatic. Endoscopic findings of gastric metastasis from breast cancer markedly vary from benign to malignant, and even in suspected malignant cases, it is often difficult to differentiate between primary and metastatic disease. We experienced a case in which an endoscopic examination performed during the treatment for metastatic breast cancer resembled an early-stage gastric cancer. A 71-year-old woman underwent curative surgery for right breast cancer 16 years previously. She underwent endoscopic submucosal dissection for early-stage gastric cancer 5 years ago. Two years ago, she developed metastatic disease in the lungs and mediastinal lymph nodes, and endocrine therapy was administered. At the same time, a follow-up endoscopy revealed a new elevated lesion, suspected to be an early-stage gastric cancer. However, histological diagnosis of the biopsy was metastasis of breast cancer. One and a half years later, a follow-up endoscopy revealed a gastric lesion that had reduced in size. She is still alive, having received a variety of systemic treatments. Patients with metastatic breast cancer are experiencing prolonged survival. Thus, follow-up endoscopy should be considered after the diagnosis of gastrointestinal metastasis considering the risk of lethal conditions, such as gastrointestinal bleeding and perforation. Our case serves as a reminder to clinicians how difficult it is to determine whether a gastric lesion is primary or metastatic based on endoscopic findings and the importance of communication with endoscopists and pathologists.