Studies on BCR-ABL expression in ET have yielded discrepant results. Some have reported expression of BCR-ABL transcripts in 21 to 63% of patients with ET [6-9], while others indicated that BCR-ABL transcripts are an incidental finding [10-14]. In our study, BCR-ABL tran­scripts were detected in only 3.6% of patients. The pres­ence of BCR-ABL transcripts was not accompanied by any other clinical or laboratory characteristic of CML, and long-term follow-up showed a clinical course typical for ET.

We did not observe any differences in clinical and laboratory features between the BCR-ABL-positive and BCR-ABL-negative patients, and almost all patients fol­lowed an uneventful course. The overall survival time did not differ between the two groups, although the number of BCR-ABL positive patients was too small to draw any firm conclusion. We observed only one transformation of ET into acute leukemia, and this occurred in a BCR-ABL negative patient. Thus, our study argues against significant involvement of the BCR-ABL gene in the pathogenesis of ET. The presence of BCR-ABL transcripts does not ex­clude the diagnosis of ET and does not appear to influence the course of the disease.