Gastric and peritoneal metastases from breast carcinoma with a mixed ductal-lobular phenotype and aberrant E-cadherin: a case report.

Gastric metastasis from breast cancer is rare and frequently misdiagnosed as primary gastric adenocarcinoma. Mixed ductal-lobular carcinoma demonstrates a unique metastatic pattern with a predilection for the gastrointestinal tract and serosal surfaces, creating significant diagnostic and therapeutic challenges. We describe a 77-year-old woman with a history of estrogen receptor-positive breast carcinoma who presented 3 years after mastectomy with epigastric pain, vomiting, and weight loss. Endoscopy revealed a malignant-appearing gastric ulcer and initial histology suggested primary gastric adenocarcinoma with signet-ring features. However, immunohistochemical analysis (pan-CK, CK7, mammaglobin, ER, PR positivity with CK20 and CDX2 negativity) confirmed metastatic breast carcinoma. Operative findings revealed diffuse peritoneal and omental metastases. The patient underwent palliative gastrojejunostomy but developed severe postoperative complications and died on postoperative day 51. This case highlights the importance of immunohistochemistry and multidisciplinary evaluation to avoid unnecessary radical surgery in metastatic breast carcinoma.