CD5+ immunophenotype in the bone marrow but not in the peripheral blood in a patient with hairy cell leukemia

We report the case of a patient with rare CD5+ hairy cell leukemia, which was unusual, as there was also a discrepancy between the bone marrow and peripheral blood immunophenotypes. We propose that some degree of maturation within the malignant clone and the predominance of more mature CD5- hairy cells in the peripheral blood can explain this observation. The patient was treated with a conventional course of cladribine (2'-chlorodeoxyadenosine) and achieved complete remission. We conclude that the unusual CD5+ immunophenotype of this patient did not affect prognosis or change the response to standard therapy.