Immunoelectron Microscopy of Megakaryoblasts in Megakaryoblastic Transformation of Chronic Granulocytic Leukemia

The cells undergoing blastic transformation of chronic granulocytic leukaemia (CGL) are considered to be of pluripotent stem cell origin [1,4]. As in acute haemoblastosis, several types of blasts may be identified by cytochemical methods [10]. In the blastic transformation of CGL, myeloblasts are predominant in about 60% and lymphoblasts in 20% of cases. The lymphoblastic and other uncommon types of transformation cannot be identified by cytochemical methods alone [12]. In the diagnosis of megakaryoblastic transformation the electron-microscopic platelet-peroxidase reaction (PPO) and antibodies against platelet glycoproteins and against factor VIII antigens may be of help. Owing to these methods the number of cases with megakaryoblastic proliferation has increased substantially in the past few years [2,6,11]. According to San Miguel et al. (1985), the frequency of megakaryoblastic transformation within the poorly differentiated types of blastic transformation of CGL exceeds 30% [9]. Electron-microscopic study of the binding of monoclonal antibodies against platelet glycoproteins makes it possible to analyse simultaneously the ultrastructural features and the immunophenotype of megakaryoblasts.