The most common sites of breast cancer metastasis are the lymph nodes, lungs, bones, and liver. Gastrointestinal (GI) metastasis is relatively rare and often occurs within several years after a breast cancer diagnosis. Most patients experience abdominal pain, anorexia, bleeding, vomiting, and other digestive system symptoms, symptoms which are difficult to distinguish from primary gastric cancer. There is no characteristic change seen under a digestive tract endoscopy, and the difference in morphology under the pathological microscope from that of primary poorly differentiated gastric adenocarcinoma is so small that it can easily cause a misdiagnosis. This paper reports the case of 46-year-old female patient whose first symptom was GI discomfort. She was hospitalized for GI surgery with an unknown medical history, but, during the preoperative examination, multiple breast masses were found on both sides, which were proved by pathology to be invasive lobular cancer. According to the medical literature, bilateral breast cancer with gastric metastasis is very rare, and, so far, this is the first reported case. Despite it being a rare phenomenon, it is necessary to be aware of the possibility of metastatic lobular carcinoma in the diagnosis of poorly differentiated gastric adenocarcinoma by biopsy.AJTR Copyright © 2021.