CD15 (Leu-M1) is a hematopoietic antigen expressed by granulocytes, monocytes, Reed-Sternberg cells, and subsets of T and B-cells.  CD15 may also be expressed in glandular or neuroendocrine epithelial cells as well as part of a panel to distinguish between metastatic adenocarcinoma (positive) and mesothelioma (negative).

CD15 stains strongly the cytoplasm of granulocytes.  CD15 is most commonly used as a diagnostic marker for classical Hodgkin lymphoma (CHL).  The combined staining of CD15 and CD30 in the appropriate morphologic setting is very specific for Hodgkin Lymphoma.  The biggest issue with this marker in the diagnosis of CHL is sensitivity.  In a well-optimized setting using a preferred clone, the sensitivity can be fairly high, ~70%.  In general when CHL cases are positive for CD15, it will stain a subset of the CD30 positive cells.

 

When this marker is not well optimized and/or using a suboptimal clone, then the negative results can not be trusted (even when expressed in background granulocytes).  Comparison analysis with a reference lab to compare IHC expression in validation cases is recommended for this antibody.  PAX-5 is also a helpful marker, when CD15 is negative and CHL is suspected, as it will be dimly expressed (compared to background B-cells) in ~90% of CHL cases.

CD15 will stain at least a subset of normal granulocytes(~90%), monocytes (30-60%), promyelocytes in the bone marrow.  A subset of cases of acute myelogenous leukemia (AML) will express CD15.  CD15 is a myeloid marker, and appears to be preferentially expressed in AML cases with monocytic differentiation (not entirely sensitive or specific).  Flow cytometry is more sensitive in detected CD15 expression than immunohistochemistry (IHC).  A subset of neoplastic T and B-cells may also express CD15.

CD15 has been used as part of a panel to differentiate between mesothelioma and adenocarcinoma.  CD15 is expressed in ~7% of epithelioid mesotheliomas and is not known to be expressed in sarcomatous mesothelioma while being expressed in a majority of adenocarcinomas (~72%).  CD15 is not typically one of the main markers used in the mesothelioma vs. adenocarcinoma panel (there are other markers with better sensitivity/specificity profiles), but may be helpful in certain circumstances.

Wick, MR. “Immunohistochemical approaches to the diagnosis of undifferentiated malignant tumor.”Annals of Diagnostic Pathology12(2008):72-84.

 

Bone Marrow IHC.  Torlakovic, EE, et. al. American Society for Clinical Pathology Pathology Press © 2009.  pp. 51.

 

Marchevsky, A. M. (2008). Application of immunohistochemistry to the diagnosis of malignant mesothelioma. Archives of Pathology & Laboratory Medicine, 132(3), 397–401. 

 

Dunphy CH, Polski JM, Evans HL, Gardner LJ. Evaluation of bone marrow specimens with acute myelogenous leukemia for CD34, CD15, CD117, and myeloperoxidase. Arch Pathol Lab Med. 2001;125: 1063–1069.