Subtle Gastric Involvement by Metastatic Breast Carcinoma During Helicobacter pylori Evaluation: A Diagnostic Pitfall and Case Report

Gastric metastases from breast carcinoma are well documented in the literature; however, they may present with extremely subtle clinical, endoscopic, and histologic findings, creating a significant diagnostic challenge. We report a case of metastatic breast carcinoma identified in a routine gastric biopsy obtained to evaluate for Helicobacter pylori infection during esophagogastroduodenoscopy performed as part of the metastatic workup, in a patient with known metastatic disease approximately 10 years after the patient’s initial breast cancer diagnosis. Endoscopic examination showed mildly congested mucosa with thickening of the gastric folds and subtle wall stiffness, but without a discrete mass lesion. Histologic examination revealed only rare discohesive atypical cells infiltrating the lamina propria, which might be difficult to recognize on routine evaluation. Immunohistochemical studies demonstrated positivity for estrogen receptors and GATA3, supporting metastatic breast carcinoma. This case is not presented as a rare occurrence of gastric metastasis, but rather as an important diagnostic pitfall. It illustrates how metastatic breast carcinoma may present as subtle cells in a gastric biopsy that might be overlooked on routine evaluation, even in a patient with known metastatic disease. In patients with a history of breast carcinoma, the presence of even minimal atypical cells in a gastric biopsy should prompt consideration of metastatic disease and appropriate immunohistochemical evaluation. Accurate determination of receptor status, including HER2-low tumors (IHC 2+/FISH-negative), remains important for therapeutic decision-making: HER2-low, hormone receptor-positive breast cancer progressed on endocrine therapy is now an indication for trastuzumab deruxtecan.