CK7 vs CK20 in IHC
CK7 and CK20 are cytokeratin stains often considered as a pair. Their pattern can orient a differential, but it cannot establish a primary site on its own.
Reviewed
The short answer
CK7 and CK20 are cytokeratin immunostains used to describe epithelial staining patterns. Reporting them as positive or negative in combination can help organize a differential, but no single CK7/CK20 pattern identifies a tumor's origin with certainty.[1][2]
How to use the paired pattern
A CK7-positive/CK20-negative pattern occurs in several tumor types, while CK7-negative/CK20-positive staining is often associated with colorectal origin in the appropriate setting. Both patterns have exceptions. The value of the pair is to suggest which more specific markers to consider next, rather than to replace morphology or clinical history.[2][1]
Where the shortcut fails
A recent retrospective review found that CK7/CK20 patterns were often inconsistent with the final diagnosis in cases where both stains were ordered. Variable expression across tumor subtypes and focal staining can make textbook pattern tables misleading. Organ-directed markers and comparison with prior specimens may be more informative.[1]
That review describes a CK7-positive/CK20-negative lung adenocarcinoma example where TTF-1 supplied more specific information. The lesson is about choosing stains for the actual differential, not treating a familiar CK7/CK20 pattern as a final answer.[1]
Relevant ReagentScope records
The ReagentScope CK7 marker page and CK20 marker page link to verified Bio SB CK7 RM284 product and CK20 Ks20.8 product records, respectively. These are product specifications, not a rule for interpreting a patient's staining pattern.[3][4]
References and sources
- Revisiting the use of CK7 and CK20 immunohistochemical stains in pathological diagnoses (scientific reference)
- Immunohistochemistry for Diagnosis of Metastatic Carcinomas of Unknown Primary Site (scientific reference)
- Bio SB Cytokeratin 7 RM284 product page (PI3764) (manufacturer product information)
- Bio SB Cytokeratin 20 Ks20.8 product page (PI5391) (manufacturer product information)