Breast cancer metastases to the stomach are very rare. As characteristics of breast cancer metastases to the stomach, metastases of lobular carcinoma, mainly with signet ring cells, are frequently observed, and they are often difficult to distinguish from a primary gastric cancer with signet ring cells. Moreover, because no characteristic symptoms are shown and they involve a submucosal lesion, it is difficult to make a radiographic diagnosis. However, if a gastric lesion is observed after breast carcinoma surgery, differentiation between a gastric primary lesion and a metastatic lesion is very important in order to determine treatment. We encountered a case that was diagnosed as early gastric cancer discovered using an endoscope 2 years after surgery and which was found to be breast cancer metastasis to the stomach by gross cystic disease fluid protein (GCDFP) and cytokeratin (CK) 7/20 immunostaining of the biopsy tissue. Here, we report our findings of this unique case.