Transplant decision-making strategies in the myeloproliferative disorders

Myelofibrosis with myeloid metaplasia, also known as idiopathic myelofibrosis (IF) or agnogenic myeloid metaplasia, is one of the characteristic manifestations of polycythemia vera (PV) in the spent phase, and has a particularly adverse prognosis. IF may also present de novo. To date, treatment strategies for both spent-phase PV and IF have frustrated both clinicians and patients, with little clear progress made over the past 50 years. Treatment modalities with some benefit in chronic myeloid leukemia (CML), such as interferon (IFN), have been used to shrink the massive organomegaly seen in these patients and to improve their marrow function, but are not curative, and not all patients respond or can tolerate the agent. A curative approach is allogeneic peripheral hematopoietic stem cell transplantation. The preparative regimens used in fully ablative techniques rule out older patients for consideration, and many younger patients with good prognostic criteria may do sufficiently well on medical treatment or observation to avoid transplantation. Older patients may have the option to undergo a human leukocyte antigen (HLA)-identical sibling transplant using a reduced intensity preparative regimen in order to minimize peritransplant mortality. Thus a prerequisite to the broad use of transplantation is objective determination of candidacy. Several evaluation methods agree that anemia, age, and cytogenetic abnormalities all predict poor survival in IF, suggesting that patients with anemia and an abnormal karyotype are the prime candidates for allogeneic transplantation. Experimental peripheral blood models that may reflect the degree of marrow fibrosis, such as the serum procollagen 3 peptide assay, have been used to determine if they are more informative of patient status than a single, random bone marrow sampling. Marrow fibrosis may be patchy, and thus a marrow biopsy alone without other data about marrow function may be misleading. Considerable long-term success in eradicating fibrosis and restoring normal cytogenetics, normal bone marrow morphology, and normal complete blood cell counts through transplantation has been reported. Many questions remain to be answered, however, before the appropriate role of hematopoietic stem cell transplantation in the setting of both spent-phase PV and IF can be determined.