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A 74-year-old woman was diagnosed with stage Ⅳ breast carcinoma at our hospital in 2016 and is currently undergoing chemotherapy. Chest and abdominal computed tomography (CT) showed axillary lymph node metastases and osteolytic bone metastases in the skull and the spine. There were no obvious metastasis in the gastrointestinal tract. In December 2022, she visited her previous doctor for treatment of anorexia. An esophagogastroduodenoscopy (EGD) conducted by her previous doctor revealed sclerosis and poor extension of the gastric wall, which indicated that it was a type 4 advanced gastric cancer (AGC; Figure 1). EGD was performed again at our facility and 8 biopsies were taken. All these biopsies showed poorly differentiated adenocarcinoma, indicating that the metastasis originated from the breast carcinoma. Furthermore, to confirm this diagnosis, the expression levels of hormone receptors in cancer tissues were examined by immunohistochemical (IHC) analyses. The proportions of estrogen- and progesterone-receptor-positive cells were 60 and 5 % (Allred’s total scores: 6 and 4), respectively. Human epidermal growth factor receptor 2 (HER2) score was estimated at 2+ (equivocal), and FISH analysis revealed no HER2 gene amplification. Ki-67 (MIB-1) labeling index was 25 % in the hot spot (so-called luminal B-like subtype). E-cadherin was mostly negative, or weakly positive, GATA binding protein 3 were diffusely positive, gross cystic disease fluid protein 15 were variously positive, and mammaglobin was focally positive. In addition, cytokeratin 7 was positive, whereas cytokeratin 20 was negative (Figures 2 and 3). Based on these pathological findings, the diagnosis of gastric metastasis derived from invasive lobular carcinoma was confirmed.
Currently, endocrine therapy for breast carcinoma contributes significantly to mortality reduction and recurrence control.1 However, the endoscopic and pathologic findings of gastric metastases derived from breast carcinomas are often mistaken to be the findings of type 4 AGC, thereby delaying correct diagnosis and therapeutic intervention. Gastric metastases derived from breast carcinomas should be especially kept in mind in cases of women with a history of breast carcinoma. Accurate endoscopic diagnosis, EGD-biopsies, and pathological examinations, including IHC, are important for differentiating between gastric metastases derived from breast carcinomas and type 4 AGCs. In addition to highlighting the importance of IHC, we have focused on another interesting point in the present study: owing to EGD-biopsies, cases of gastric metastases derived from breast carcinomas are easier to diagnose than cases of type 4 AGCs. In our current case, cancer tissue was abundant in all eight biopsy specimens. In the case of type 4 AGC, the diagnosis of adenocarcinoma using EGD-biopsy specimens is not so common, as clinical reports have shown that the proportion of definitive diagnoses made on the basis of EGD-biopsy results is approximately 50 %.2, 3 In the future, examining the proportion of diagnosis by EGD-biopsies in both may contribute to the rapid diagnosis of gastric metastases derived from breast carcinomas.