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 leukemic cells were detected in the spleen 3½ months before clinical or laboratory evidence of the onset of the acute leukemia.