An otherwise typical case of non-Japanese hairy cell leukemia with CD10 and CDw75 expression: response to cladaribine phosphate therapy.

Hairy cell leukemia (HCL) in Western patients typically expresses CD19, CD20, CD11c, CD25, HLA-DR, and IgG/lambda and lacks expression of CD5 and CD10. The immunophenotype is in contrast to Japanese HCL which typically expresses CD5 and CD10. Western and Japanese HCL also differ in their clinical presentation and response to treatment with alpha-interferon. We report a case of non-Japanese HCL which presented typically with pancytopenia; however, the immunophenotype was atypical with expression of CD10 and CDw75. CDw75 expression has not previously been described in either Japanese or non-Japanese HCL. The patient achieved a marked partial pathologic response and complete clinical response to treatment with cladaribine phosphate.