A novel variant of B-lymphoid leukemia expressing kappa/lambda light chains.

We studied a patient with an indolent leukemia which behaved similarly to chronic lymphocytic leukemia (CLL). Leukemic cells, however, showed larger cell diameters and lower nuclear/cytoplasmic ratios than typical CLL cells, and contained numerous cytoplasmic vacuoles. The cells also demonstrated some morphologic characteristics of hairy cell leukemia. Furthermore, flow-cytometric analysis demonstrated a distinct population of kappa/lambda double-positive tumor cells, as well as kappa single and lambda single populations. Southern blot analysis confirmed rearranged bands for both light chains with a monoclonal heavy chain rearrangement. Despite a decision not to treat this asymptomatic patient, disease progression was not observed. This case may represent a unique variant of B lymphoid leukemia. Possible mechanisms of abnormal light chain expression are discussed.