IMMUNOPHENOTYPE AND ULTRASTRUCTURAL STUDIES IN BLAST CRISIS OF CHRONIC MYELOID-LEUKEMIA

Thirty-four patients with chronic myeloid leukemia in blast crisis (CM L-BC) were evaluated for lineage differentiation, with immunological m arkers and the presence of ultrastructural peroxidase. Eighteen (52.9% ) were found to have myeloid blast crisis. Cytochemically, myeloperoxi dase (MPO) could be detected only in six patients on light microscopy while in the remaining 12 patients, myeloid differentiation was confir med only by demonstration of MPO either at ultrastructural level or by the reactivity with anti myeloperoxidase (anti MPO) antibody. Six (17 .6%) had lymphoid blast crisis as identified by lymphoid specific mark ers (CD19; CD10; CD7; CD4) along with the absence of myeloid markers, Heterogenous blast cell populations with mixed lineage differentiation were seen in 4 (11.7%) patients. These cases showed both lymphoid (Cd 19, CD10) and myeloid (anti MPO and ultrastructural MPO) characteristi cs. A single case of megakaryoblastic blast crisis was identified with positivity for CD41 and CD42 along with the presence of platelet pero xidase at the ultrastructural level, Five cases (14%) of CML blast cri sis remained unclassifiable. These results suggest that blast crisis i n CML show an arrest of differentiation at an early stage when compare d to de novo acute leukemias. This is particularly evident from the fa ct that MPO could only be demonstrated ultrastructurally or with anti MPO antibody in the majority of patients with myeloid differentiation. It is expected that utilisation of molecular studies including immuno globulin and T-cell receptor gene rearrangement and m-RNA expression f or myeloperoxidase will provide a better insight into the level of dif ferentiation for the presently unclassifiable cases of CML-blast crisi s.