CK7

CK7 (Cytokeratin 7) is a protein found in the structural skeleton of certain epithelial and mesothelial cells. Pathologists detect it using a stain called immunohistochemistry on biopsy tissue to help figure out what type of cell a tumor came from. It is one of several markers used together, not a stand-alone test, when working up a suspected mesothelioma or metastatic cancer.

Origin

Cytokeratins were catalogued in the early 1980s by Moll and colleagues, who numbered 20 different keratin proteins (CK1 through CK20) based on their size and charge on a gel. CK7 was assigned within that numbering system and quickly became a routine immunohistochemistry marker in diagnostic pathology.

Significance in Asbestos Context

For patients with a suspected mesothelioma, CK7 staining helps confirm that the tumor is of epithelial or mesothelial origin rather than, for example, a lymphoma, melanoma, or sarcoma, cancers that are treated very differently. Mesotheliomas are typically CK7-positive, but so are many lung adenocarcinomas and other carcinomas, so CK7 alone cannot distinguish mesothelioma from a lung cancer that has spread to the pleura. That distinction matters both medically (treatment plans differ) and legally (mesothelioma claims have different evidentiary requirements than lung cancer claims), which is why your pathology report should also include mesothelial-specific markers such as calretinin, WT-1, D2-40, and carcinoma markers such as CK5/6, TTF-1, Claudin-4, and BerEP4.

Example Sentence

Her immunohistochemistry panel showed the tumor was CK7-positive and CK20-negative, and the addition of calretinin and WT-1 positivity supported the final diagnosis of epithelioid mesothelioma.

Related Terms

Immunohistochemistry, Calretinin, WT-1, Cytokeratin 5/6, TTF-1, Epithelioid Mesothelioma

Notes

• Ask your pathologist or oncologist for a copy of the full immunohistochemistry panel, not just the CK7 result, because mesothelioma diagnosis requires a combination of positive and negative markers.
• If CK7 is the only marker reported, request that the tissue block be sent for additional mesothelial and carcinoma markers before treatment decisions are finalized; this is standard of care under the most recent International Mesothelioma Interest Group guidelines.
• Preserve the original pathology report and the paraffin tissue block (held by the hospital lab). These may be needed for a second opinion at a mesothelioma specialty center and for any future legal claim.
• A CK7-positive, CK20-negative pattern is common to both mesothelioma and lung adenocarcinoma, so do not assume the diagnosis based on CK7 alone.