[Histopathology and molecular pathology of chronic myeloproliferative disorders]

Diagnosis of chronic myeloproliferative disorders (CMPD) can encounter difficulties due to overlaps and possible transitions between the different entities and their similarity to reactive myeloproliferations. In this study DNA analysis has been applied to improve differentiation of CMPD. All subtypes of CMPD analyzed, including chronic myeloid leukemia (CML), agnogenic myeloid metaplasia (AMM), polycythemia vera (PV), and essential thrombocythemia (ET), had in common that granulocytes and bone marrow cells were clonal in origin as shown by X-chromosome-linked DNA polymorphism in conjunction with methylation patterns. Reactive myeloproliferations, by contrast, revealed a polyclonal inactivation pattern. Clonality could not distinguish CMPD from cases of myelodysplastic syndrome (MDS) since the latter also exhibited clonal hematopoiesis. AMM belongs to the group of myeloproliferative syndromes. Up to now the cellular phase at onset of the disease (megakaryocytic myelosis) has not been analyzed for clonality of the hematopoietic cells. Granulocytes as well as bone marrow cells from the cellular phase and advanced stages of the disease revealed a monoclonal inactivation pattern of X-chromosomal genes. These results show that the cellular phase already represents a monoclonal, and hence probably a neoplastic, proliferation of a pluripotent stem cell. The monoclonality of granulocytes could also be demonstrated in patients with splenomegaly and strongly argues against a compensatory proliferation of regular hematopoiesis in this organ. Because of their clonal origin, peripheral granulocytes were used in all cases (n = 244) for the detection of bcr-gene rearrangement. Despite possible morphological overlaps between different types of CMPD, bcr-gene rearrangement proved to be specific for CML and could be applied to differentiate CML from other CMPD in cases of uncertain morphological diagnosis. It is concluded that CMPD represent clonal hemopoietic disorders that probably have specific underlying genetic defects. Thus, DNA analysis can substantially aid in the differential diagnosis of CMPD.