CD45 | PathMD

CD45 (LCA) is also known as leukocyte common antigen (LCA). It is a sensitive marker for lymphoid cells. In the most general form it is often used as part of a panel for undifferentiated tumors or so-called “small round blue cell tumors.” Such a screening panel usually includes:

CD45 (lymphoid)
AE1/AE3 (carcinoma/epithelial)
S-100 (neural/melanocytic)
Desmin (sarcoma/muscular origin)
CD99 (PNET if other markers are negative).

The biggest pitfall is to remember that CD45 is not perfectly sensitive. Anaplastic large cell lymphoma (ALCL) may not express CD45 in 1/4th to 1/3rd of cases. Classical Hodgkin Lymphoma cells are “classically” negative for CD45. Mature plasma cells/plasma cell neoplasms are usually negative for CD45 (CD138 will also stain epithelial cells in addition to plasma cells).

Photomicrographs

CD45 - Classical Hodgkin Lymphoma — Loss of CD45 expression in Hodgkin cells in a case of nodular sclerosing classical Hodgkin lymphoma (CHL).

CD45 - Non-Hodgkin Lymphoma — Strong diffuse expression of CD45 in a non-Hodgkin lymphoma.

References

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