胃転移を認めた乳腺浸潤性小葉癌の１例

A 45-year-old woman underwent total mastectomy with axillary lymph node dissection for right breast cancer in 2015. Histopathological examination of the resected specimen showed triple-negative invasive lobular carcinoma and advanced lymph node metastasis. The patient underwent postoperative adjuvant therapy consisting of a dose-dense epirubicin-cyclophosphamide regimen and weekly paclitaxel and radiotherapy. However, multiple bone metastases were detected, 18 months postoperatively. The patient developed upper abdominal discomfort, 21 months postoperatively, and gastroscopy revealed multiple, irregular depressed lesions in the stomach. Histopathological examination of stomach biopsy specimens revealed tumor cells that showed diffuse invasion of the lamina propria of mucous membrane. Immunohistochemical evaluation of biopsy specimens obtained from the stomach and the excised breast tissue showed cells that were immunopositive for CK7 and GCDFP-15 and immunonegative for CK20. The gastric lesion was therefore diagnosed as metastases from invasive lobular carcinoma of the breast. Although the patient received chemotherapy, she died of meningeal carcinomatosis from breast cancer, 7 month after the diagnosis of stomach metastasis.
Immunohistochemical evaluation for CK20, which is expressed in gastric cancer and GCDFP-15, which originates from breast tissue, is useful to distinguish between breast cancer metastases and signet ring cell carcinoma of the stomach.