RECOGNITION OF HAIRY-CELL LEUKEMIA IN A SPLEEN OF NORMAL WEIGHT - THE CONTRIBUTION OF IMMUNOHISTOLOGIC STUDIES

A 68-year-old man with known hairy cell leukemia (HCL) underwent splenectomy; the spleen weighed only 140 g. Microscopic examination of the spleen revealed no clear diagnostic evidence of HCL, but there was an unusual and suspicious subendothelial lymphoid filtration of the trabecular veins. Cell suspension studies also were not diagnostic because a monoclonal B-cell population could not be defined. Alternatively, when we focused on the subendothelial infiltrate in the frozen sections prepared for immunohistochemical studies, the findings indicated that the subendothelial cells were monoclonal B-cells (IgG, kappa). Staining with monoclonal antibodies disclosed the phenotype Tac+, Leu-14+, Leu-M5+, B2-, BA-1-, and BA-2, a phenotype characteristic of HCL. In this case, an unusual but nondiagnostic morphologic finding provided guidance for the correlative immunophenotypic analysis of the same site in frozen sections and thereby allowed a definitive diagnosis.