B-acute lymphoblastic leukemia (B-ALL) is a neoplasm of precursor lymphoid cells committed to the B-lineage. Expression of CD5 is rare in B-ALL.
We studied the clinicopathologic, immunophenotypic, and molecular genetic features of 10 cases of B-ALL with aberrant CD5 expression, and compared with CD5-B-ALL.
B-ALL with aberrant CD5 expression is rare and predominantly affects men. Patients with CD5+ B-ALL had shorter median overall survival (21 vs 45 months, P = .0003). Expression of CD5 imposed a challenge in the differential diagnoses between B-ALL and other CD5+ B-cell lymphomas with blastic morphology. Dim CD20 and CD45, lack of surface immunoglobulin, expression of CD34 and TdT, negative immunostain for cyclin D1, and absence of t(11;14)(q13;q32) support a diagnosis of B-ALL.
CD5 expression is rare in B-ALL and associated with poor clinical outcome. CD5+ B-ALL represents a distinct entity that needs to be considered in the differential diagnoses of CD5+ B-cell lymphoproliferative disorders.

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