Invasive Lobular Carcinoma with Gastric Metastasis Mimicking Linitis Plastica as the First Presentation: A Case Report

Invasive lobular carcinoma (ILC) can metastasize to the gastrointestinal tract and closely mimic primary gastric adenocarcinoma, especially when signet-ring cell morphology is present. Here, we report the case of a 65-year-old woman who presented with epigastric discomfort and abdominal fullness. Esophagogastroduodenoscopy showed multiple skipped mucosal lesions in the stomach, and an endoscopic biopsy revealed poorly differentiated adenocarcinoma with signet-ring cell features. She was initially diagnosed as having primary gastric cancer, with imaging showing multiple bone metastases. Later, a newly detected breast lump was diagnosed as ILC on core needle biopsy, which was positive for estrogen receptor (ER) and progesterone receptor, but negative for HER2. As no signet-ring cells were found, the initial assumption was double primary cancers of the stomach and breast. Accordingly, the multidisciplinary team discussion concluded that the breast lump represented a second primary, early-stage breast cancer, making lumpectomy and sentinel lymph node biopsy appropriate to achieve local control and prevent progression-related complications. Subsequent lumpectomy revealed ILC with signet-ring cell morphology, prompting re-evaluation of the gastric biopsy with extended immunohistochemistry, which confirmed metastatic breast origin (ER+, GATA3+, HNF4α–). Therefore, the diagnosis was revised to stage IV ILC with gastric and bone metastases. This case highlights the diagnostic challenges posed by ILC with gastric metastases exhibiting signet-ring cell morphology, and emphasizes the importance of integrating clinical history with careful, parallel pathological and immunohistochemical evaluations.