Atypical hairy cell leukemia

The morphologic differential diagnosis of mature B-cell neoplasms with cytoplasmic projections includes splenic lymphoma with vicious lymphocytes and hairy cell leukemia. Although the classification of hairy cell leukemia is not universally recognized, 3 variants have been described, namely, classic, variant, and Japanese variant, each of which has different clinical and immunophenotypic features. Classic hairy cell leukemia is virtually always CD11c⁺, CD25⁺, and CD103⁺. Variant and Japanese variant hairy cell leukemias are usually CD11c⁺, always CD25^-, and occasionally CD103⁺. Each variant is characteristically CD10^-. We present a case of hairy cell leukemia with a unique immunoprofile in that the cells were CD10⁺, CD25⁺, and CD103^-, and we review the criteria helpful in differentiating 'hairy' B-cell neoplasms. This case empha-sizes the variability of hairy cell leukemia anti the need to correlate all clinical and pathologic data in reaching a diagnosis.