The differentiation between primary gastric cancer and a metastatic breast tumor to the stomach is important for planning of treatment and to spare the patient unnecessary surgery. We report a rare case of breast cancer with metastasis to the stomach. The diagnosis was established by histologic and immunohistochemical analyses of biopsies of the stomach lesion using gross cystic disease fluid protein-15, cytokeratin, carcinoembryonic antigen, and epithelial membrane antigen. Positivity for gross cystic disease fluid protein-15 with negative staining for carcinoembryonic antigen supported the diagnosis of a breast cancer metastasis. The patient was treated with systemic chemotherapy without surgery and is still alive 2 years after initial referral for a gastric neoplasm.