Simultaneous gastric and colonic metastasis of invasive lobular carcinoma of the breast.

Breast cancer commonly metastasizes to the lungs, bones, liver, and brain; however, gastrointestinal involvement is uncommon. Simultaneous metastases to both the stomach and colon are extremely rare. We report the case of a 53-year-old woman with bilateral breast cancer (right invasive ductal carcinoma and left invasive lobular carcinoma [ILC]) who developed gastric and colonic metastases, presenting with rare endoscopic findings characterized by multiple polypoid lesions, along with disseminated carcinomatosis of the bone marrow. Biopsies from the stomach and colon revealed poorly differentiated adenocarcinomas that were estrogen receptor-positive and negative for E-cadherin in the colon, consistent with ILC metastases. Endocrine therapy with letrozole led to systemic improvement. However, diarrhea and abdominal pain persisted until palbociclib was initiated, after which both symptoms markedly improved. Follow-up endoscopy demonstrated regression of the gastric and colonic lesions. This case is of educational value because it demonstrates, with high-quality images, subtle mucosal changes with a polypoid appearance that are not widely recognized as typical findings of colonic metastasis from ILC, and includes a review of previously reported cases. In patients with breast cancer, particularly ILC, persistent gastrointestinal symptoms may suggest metastasis. Careful endoscopic evaluation with biopsy is essential for diagnosis and monitoring the treatment response.