Gastric Metastases From Invasive Breast Lobular Carcinoma, Identified by [<scp>¹⁸F</scp>]<scp>FDG PET</scp>/<scp>CT</scp>, 20 Years After Primary Diagnosis: A Case Report

Invasive lobular carcinoma (ILC) of the breast is a rare subtype of breast cancer with distinct metastatic patterns. Although gastrointestinal metastases are rare, they can occur years after initial treatment. This case highlights the diagnostic challenges and management of late-onset gastric metastases. A 68-year-old woman with a history of ILC treated 20 years earlier presented with elevated tumor markers. [¹⁸F]fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) revealed hypermetabolic lesions in the stomach and esophagus in this patient with previously diagnosed gastritis and gastroesophageal reflux disease. Endoscopy and biopsies confirmed the presence of metastatic ILC in the stomach. Adjustment of treatment, including exemestane and everolimus, followed by paclitaxel and tamoxifen, resulted in partial disease control. Late-onset gastrointestinal metastases of ILC are uncommon and require special vigilance, particularly in patients with associated benign gastrointestinal pathologies, which may delay diagnosis. Persistent or new-onset gastrointestinal symptoms in breast cancer patients warrant thorough evaluation, including FDG PET/CT imaging and histological confirmation.