[A Case of Two Episodes of Intraperitoneal Metastasis after Surgery for Breast Cancer].

The patient is an 83-year-old woman who underwent a right mastectomy with axillary lymph node dissection in 2009. The histological type was invasive lobular carcinoma, and the pathological stage was diagnosed as pStage Ⅲc. She received chemotherapy, radiotherapy, and 5 years of endocrine therapy. In 2019, a tumor in the ascending colon was discovered during a routine check-up. Laparoscopic right hemicolectomy was performed, and pathological examination confirmed the tumor was a metastasis from breast cancer. she was undergoing endocrine therapy(letrozole)at the time. In 2024, the patient presented with loss of appetite and epigastric pain after meals. Upper gastrointestinal endoscopy suggested type 4 advanced gastric cancer, and biopsy confirmed poorly to undifferentiated adenocarcinoma. While metastasis from breast cancer was considered, biopsy findings alone made it difficult to differentiate from primary gastric cancer. Therefore, a laparoscopic distal gastrectomy was performed for oral intake management. Pathological examination confirmed gastric metastasis from breast cancer. In patients with a history of breast cancer, the possibility of metastasis should be considered. Comparative histological analysis and immunohistochemical studies are essential for accurate diagnosis.