KRT7 and signet ring cell carcinoma: It has been hypothesized that when a signet ring cell adenocarcinoma is revealed on colon biopsy, the diagnosis of a colonic origin is supported by the presence of a CK7−/CK20+ staining pattern in the neoplastic cells, while a gastric origin is diagnosed when the cells have a CK7+/CK20 staining pattern (15).