CD5

CD5 is a T-cell marker, although it is the least specific of the group (CD2, CD3, CD4, CD5, CD7, and CD8).  CD5 co-expression on B-cells is characteristic of certain lymphomas, specifically CLL/SLL and Mantle Cell Lymphoma.  A subset of DLBCLs may also express CD5, although there may be a question as to if that represents de novo lymphoma vs.  “transformed” CLL/SLL or Mantle Cell Lymphoma.
 
The expression level of CD5 will often be less than the expression on background T-cells in cases of CLL/SLL and Mantle Cell Lymphoma, and this expression differentiation may be helpful by both IHC and flow cytometry.
CD5 Expression
Many different B and T-cell lymphomas have reported CD5, and while it is a useful marker, specificity should be determined with a broader set of markers in addition to the morphology of the lymphoma.  Molecular studies may also be helpful.

Photomicrographs
CD5 - Benign Tonsil
CD5 – Benign Tonsil
CD5 - Mantle Cell Lymphoma
CD5 – Mantle Cell Lymphoma
CD5 - CLL/SLL
CD5 – CLL/SLL
CD5 - Benign Tonsil
CD5 – Benign Tonsil

References
Dong HY, Gorczyca W, Liu Z, Tsang P, Wu CD, Cohen P, et al. B-cell lymphomas with coexpression of CD5 and CD10. Am J Clin Pathol. 2003;119: 218–230. doi:10.1309/U98A-DVKU-C26R-2RJA
 
Gao J, Peterson L, Nelson B, Goolsby C, Chen Y-H. Immunophenotypic variations in mantle cell lymphoma. Am J Clin Pathol. 2009;132: 699–706. doi:10.1309/AJCPV8LN5ENMZOVY
 
Dalton RR, Admirand JH, Medeiros LJ. Small Lymphocytic Lymphoma. Pathology Case Reviews. 2004;9: 7.
 
Jaso JM, Yin CC, Wang SA, Miranda RN, Jabcuga CE, Chen L, et al. Clinicopathologic Features of CD5-Positive Nodal Marginal Zone Lymphoma. Am J Clin Pathol. 2013;140: 693–700. doi:10.1309/AJCPEMVXES72DUIF
 
Went P, Zimpfer A, Tzankov A, Dirnhofer S. CD5 expression in de novo diffuse large B-cell lymphomas. Annals of Oncology. 2009;20: 789–790. doi:10.1093/annonc/mdn793
 
Cook JR. Nodal and leukemic small B-cell neoplasms. Mod Pathol. 2013;26 Suppl 1: S15–28. doi:10.1038/modpathol.2012.180
 
Bone Marrow IHC.  Torlakovic, EE, et. al. American Society for Clinical Pathology Pathology Press © 2009.  pp. 27.