CD34

CD34 is a protein found on the surface of certain cells, including blood vessel lining cells (endothelial cells), early blood-forming stem cells, and some connective tissue (fibroblastic) cells. Pathologists detect CD34 using a stain called immunohistochemistry to help identify what kind of cells make up a tumor or tissue sample. In tumors, the presence or absence of CD34 is a clue used to tell one cancer type from another.

Origin

CD34 was identified in the 1980s and named under the international "Cluster of Differentiation" (CD) system, which assigns numbered labels to cell-surface molecules recognized by specific antibodies. The molecule was first characterized on hematopoietic stem cells and later found on endothelial and certain stromal cells.

Significance in Asbestos Context

CD34 staining is part of the pathology workup that helps distinguish mesothelioma from other tumors that can look similar under the microscope, particularly solitary fibrous tumor of the pleura, vascular tumors (like angiosarcoma), and certain sarcomas, all of which can arise in the chest or abdomen and mimic mesothelioma. Mesothelioma cells are typically CD34-negative, while solitary fibrous tumors are strongly CD34-positive, so this single marker can change the diagnosis entirely. Because mesothelioma diagnosis depends on a panel of stains rather than any one test, CD34 results appear in the pathology report alongside markers like calretinin, WT-1, cytokeratin, and STAT6. Getting this differential right matters not only for treatment but also for an asbestos claim, because compensation programs and trusts require a confirmed mesothelioma diagnosis.

Example Sentence

The pathology report noted that the pleural tumor was CD34-negative and calretinin-positive, supporting a diagnosis of epithelioid mesothelioma rather than a solitary fibrous tumor.

Related Terms

Immunohistochemistry, Calretinin, Solitary Fibrous Tumor, Mesothelioma, STAT6, WT-1

Notes

• Ask your oncologist or pathologist for a copy of the full immunohistochemistry panel. CD34 status is one of several markers used together to confirm mesothelioma.
• If your initial biopsy was read at a community hospital, request a second opinion from a mesothelioma-experienced pathology center (such as a National Cancer Institute–designated cancer center) before starting treatment or filing claims.
• Preserve all pathology reports, slides, and tissue blocks; trusts, VA claims, and lawsuits typically require the original pathology documentation, and slides may be needed for re-review.
• A CD34-positive result does not rule out an asbestos-related condition entirely, but it usually points away from mesothelioma. Discuss with your doctor what the alternative diagnosis means for prognosis and for any legal claim.