Pathogenic markers in essential thrombocythemia.

Although long recognized as a clinical entity, the diagnosis of essential thrombocythemia (ET) still relies on the exclusion of reactive conditions and other myeloproliferative disorders. Recent studies have attempted to identify new markers for this disorder and suggest that part of the problem may relate to its heterogeneity. Cytogenetic abnormalities are rare, but analysis using X-chromosome inactivation patterns indicates that nearly 50% of evaluable patients have polyclonal myelopoiesis and this is associated with a lower risk of thrombosis. Reduced and heterogeneous staining of c-Mpl in bone marrow biopsies may help to distinguish ET and a reactive thrombocytosis. Increased expression of PRV-1 (polycythemia ruba vera) in granulocytes may assist in discriminating between polycythemia vera and at least some cases of ET. The contribution of these markers to disease pathogenesis is unknown and prospective studies are needed to evaluate their usefulness for predicting clinical outcome and directing patient therapy.