Acute lymphocytic leukemic transformation of chronic lymphocytic leukemia: substantiation by flow cytometry.

Acute leukemia, during the course of chronic lymphocytic leukemia, is a rare event and only a small fraction of such cases have been shown to be true transformations to acute lymphocytic leukemia. In one previous case, evidence suggested this was transformation of a single neoplastic clone. The present report describes the clinical and laboratory findings in a case of chronic lymphocytic leukemia in which an acute leukemic pattern evolved. The fluorescence-activated cell sorter provided the resolution needed to distinguish low numbers of surface immunoglobulins on the acute leukemic cells, verifying their identity as B lymphoblasts. Furthermore, a small population of large cells bearing the same light chain type as the acute leukemia cells were detected in the spleen 3 1/2 months before clinical or laboratory evidence of the onset of the acute leukemia.