In this case, the immunohistochemistry of gastric metastasis was ER (90%), PR (-), Ki67 (2%), GATA3 ( +), CK (AE1/AE3) ( +), CK7 ( +), and CK20 (-), suggesting that the tumor originated from the breast and was considered as gastric metastasis of invasive lobular carcinoma of the breast. The gene discussed is KRT20; the disease is neoplasm.