Molecular analysis of Philadelphia positive essential thrombocythemia

Seven patients with Philadelphia (Ph) chromosome positive essential thrombocythemia (ET) were investigated for the presence of a rearrangement within the major breakpoint cluster region (M-bcr) using the Southern blot technique and, in six cases, for the presence of the hybrid bcr-abl mRNA using the polymerase chain reaction (PCR). The molecular studies showed rearrangement of M-bcr in all cases; there was evidence of the b2a2 mRNA junction in one case and of b3a2 junction in five cases. These findings are identical to what might have been expected in Ph-positive chronic myeloid leukemia. These features may explain the poor prognosis of Ph-positive ET in comparison with cytogenetically normal cases. Conversely, the differences in clinical presentation may be due to other genetic changes.