Differential diagnosis of unknown primary cancers based upon immunostaining for cytokeratin (CK) 7 and 20

CK7+ CK20+

Urothelial tumors

Mucinous ovarian cancer

Pancreatic or biliary cancer

CK7+ CK20-

Non-small cell lung cancer

Small cell lung cancer

Breast cancer

Endometrial cancer

Nonmucinous ovarian cancer

Mesothelioma

Squamous cancer of cervix

Pancreatic or biliary cancer

CK7- CK20+

Colorectal cancer

Merkel cell cancer

CK7- CK20-

Hepatocellular cancer

Renal cell cancer

Prostate cancer

Squamous cell lung cancer

Head and neck cancer

CK: cytokeratin; +: positive; -: negative.

Modified from: Dabbs D. Diagnostic Immunohistochemistry, 2nd ed, Churchill Livingstone, Philadelphia, PA 2006.

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