CK7 positive and CK20 positive immunostaining favors which organ systems?

• A. Biliary tract, pancreas, stomach, bladder
• B. Liver, kidney, prostate
• C. Stomach, esophagus, colon
• D. Pancreas, liver, kidney

Answer: (A)

Immunostaining for CK7 and CK20 helps narrow down tumor origin because different tissues have characteristic patterns of these cytokeratins. A pattern where both CK7 and CK20 are positive is especially associated with tumors from glandular and urothelial tissues, including the biliary tract, pancreas, stomach, and bladder.

CK7 is commonly found in biliary epithelium, pancreatic ducts, and gastric mucosa, while CK20 is typical of urothelial lining and lower GI tract. When a tumor shows both markers, it points toward organs where both proteins are frequently expressed in carcinomas, which explains why biliary tract, pancreas, stomach, and bladder are the best match.

In contrast, colorectal cancers are typically CK20 positive but CK7 negative, and many liver and kidney tumors do not show this CK7+/CK20+ profile as consistently. Therefore, the combination CK7 positive and CK20 positive best favors the biliary tract, pancreas, stomach, and bladder.