A 45-year-old female patient presented for the evaluation of intermittent abdominal pain and weight loss (15 kg over 4 months). The patient recently underwent a needle biopsy for a 2 cm-sized mass in the right breast (Fig. 1A) and was diagnosed with invasive lobular carcinoma. On endoscopy, diffusely nodular, enlarged folds with hyperemia were observed on the greater curvature of the gastric body (Fig. 1B). On air inflation, the stomach maintained relatively good distensibility. Endoscopic ultrasonography revealed the thickening of the submucosal layer (Fig. 1C). Endoscopic biopsy using a bite-on-bite technique revealed only chronic gastritis; therefore, a strip biopsy was performed. Discohesive tumor cells had infiltrated the submucosa of the stomach (Fig. 2A), and the tumor cells were immunopositive for gross cystic disease fluid protein-15, human milk fat globule protein membrane-2, estrogen receptor, and progesterone receptor (Fig. 2B). These results were consistent with the histopathological findings of the right breast cancer. Therefore, the gastric lesion was diagnosed as a metastasis of breast cancer to the stomach. The patient underwent a radical mastectomy for right breast cancer, but gastrectomy was impossible owing to the presence of metastatic nodules in the small bowel and peritoneum. At the time of writing this report, the patient is receiving systemic chemotherapy (paclitaxel 175 mg/m² every 3 weeks).