Gastric metastasis from invasive lobular breast cancer, mimicking primary gastric cancer: A case report

RATIONALE: Gastric metastasis from invasive lobular breast cancer is relatively rare, commonly presented among multiple metastases, several years after primary diagnosis of breast cancer. Importantly, gastric cancer that is synchronously presented with lobular breast cancer can be misdiagnosed as primary gastric cancer; therefore, accurate differential diagnosis is required. PATIENT CONCERNS: A 39-year-old woman was visited to our hospital because of right breast mass and progressive dyspepsia. DIAGNOSES: Invasive lobular carcinoma of breast was diagnosed on core needle biopsy. Gastroscopy revealed a diffuse scirrhous mass at the prepyloric antrum and diagnosed as poorly differentiated adenocarcinoma on biopsy. Synchronous double primary breast and gastric cancers were considered. Detailed pathological analysis focused on immunohistochemical studies of selected antibodies, including those of estrogen receptors, gross cystic disease fluid protein-15, and caudal-type homeobox transcription factor 2, were studied. As a result, gastric lesion was diagnosed as metastatic gastric cancer originating from breast. INTERVENTIONS: Right breast conserving surgery was performed, and duodenal stent was inserted under endoscopic guidance to relieve the patient's symptoms. Systemic chemotherapy with combined administration of paclitaxel and trastuzumab was initiated. OUTCOMES: Forty-one months after the diagnosis, the patient is still undergoing the same therapy. No recurrent lesion has been identified in the breast and evidence of a partial remission of gastric wall thickening has been observed on follow-up studies without new metastatic lesions. LESSONS: Clinical suspicion, repeat endoscopic biopsy, and detailed histological analysis, including immunohistochemistry, are necessary for diagnosis of metastatic gastric cancer from the breast.