CD5-positive B-cell acute lymphoblastic leukemia.

CD5-positive B-cell acute lymphoblastic leukemia (ALL) is an exceedingly rare entity, with only a single case report in the literature. We report 2 additional cases of CD5-positive B-cell ALL in a 16-year-old male and a 15-year-old female. The 1st case was initially misdiagnosed as Ewing sarcoma due to a lack of CD45 expression and weak expression of CD99. Cytogenetic analysis of the 2nd case revealed trisomy 22, the 1st time this finding has been reported in ALL. Both patients had poor outcomes, as did the patient in the previously published case report. We conclude that CD5-positive B-cell ALL is a rare, aggressive malignancy with a poor prognosis that presents in adolescence. Pathologists and clinicians should be aware of this entity to avoid confusion with other small blue-cell tumors.