CDX2 and Merkel cell skin cancer: In summary, the potential origins of CK7−/CK20+ CUPs are limited: most often colorectal (or digestive), non-digestive intestinal (bladder), or endocrine (Merkel cell carcinoma and small cell carcinoma of salivary glands), requiring a limited antibody panel to distinguish them: CDX2 (+/− SATB2), endocrine markers and MCPyV.