Evidence-based management of polycythemia vera

Re-evaluation of hematocrit as a determinant of thrombotic risk in erythrocytosis

Here we critically evaluate the role of elevated hematocrit as the principal determinant of thrombotic risk in polycythemia and erythrocytosis, defined by an expansion of red cell mass. Since red cell volume determination is no longer readily available, in clinical practice, polycythemia and erythrocytosis are defined by elevated hemoglobin and hematocrit. Thrombosis is common in Chuvash erythrocytosis and polycythemia vera. Although the increased thrombotic risk is assumed to be due to the elevated hematocrit and an associated increase in blood viscosity, thrombosis does not accompany most types of erythrocytosis. We review studies indicating that the occurrence of thrombosis in Chuvash erythrocytosis is independent of hematocrit, that the thrombotic risk is paradoxically increased by phlebotomy in Chuvash erythrocytosis, and that, when compared to chemotherapy, phlebotomy is associated with increased thrombotic risk in polycythemia vera. Inherited and environmental causes that lead to polycythemia and erythrocytosis are accompanied by diverse cellular changes that could directly affect thrombotic risk, irrespective of the elevated hematocrit. The pressing issue in these disorders is to define factors other than elevated hematocrit that determine thrombotic risk. Defining these predisposing factors in polycythemia and erythrocytosis should then lead to rational therapies and facilitate development of targeted interventions.

Whole-blood transcriptional profiling of interferon-inducible genes identifies highly upregulated IFI27 in primary myelofibrosis

Gene expression profiling studies have unraveled deregulation of several genes that might be of pathogenetic importance for the development and phenotype of the Philadelphia-negative chronic myeloproliferative neoplasms. In the context of interferon-alpha2 as a promising therapeutic agent, we focused upon the transcriptional profiling of interferon-associated genes in patients with essential thrombocythemia (ET) (n = 19), polycythemia vera (PV) (n = 41), and primary myelofibrosis (PMF) (n = 9). Using whole-blood transcriptional profiling and accordingly obtaining an integrated signature of genes expressed in several immune cells (granulocytes, monocytes, B cells, T cells, platelets), we have identified a number of interferon-associated genes to be significantly deregulated but with a highly significant deregulation of interferon-inducible gene 27 (IFI27) (ET, PV, and PMF, fold change 8, 16, and 30, respectively). The striking deregulation of IFI genes may reflect a hyperstimulated but insufficient immune system being most enhanced in patients with advanced myelofibrosis, in whom the IFI27 gene displayed an exceedingly high expression. The interferon signature may reflect primary myelofibrosis as the burn-out phase of chronic inflammation which ultimately elicits clonal evolution and expansion owing to an exaggerated but incompetent antitumor immune response. Finally, IFI27 may be a novel biomarker of disease activity and tumor burden in patients with CMPNs.

Hydroxyurea induced acute elevations in liver function tests

Hydroxyurea (HU) is a ribonucleotide reductase inhibitor used to treat myeloproliferative diseases including polycythemia vera (PV) and essential thrombocythemia (ET). We describe an 82-year-old male who was started on HU 500 mg three times weekly for the treatment of PV. Eight days after initiation of HU he experienced anorexia, nausea, vomiting, fever, fatigue, dizziness, and shaking chills. Discontinuation of the HU resulted in resolution of his symptoms within 2 days, and HU was re-started. Ten days after re-starting HU, the patient re-presented with nausea and anorexia. Lab tests revealed elevations in liver enzyme function tests, which resolved promptly after cessation of HU. Patients being initiated on HU should be advised that rarely, fevers, chills, nausea, and elevations in liver function tests may occur. J Oncol Pharm Practice (2008) 14: 61—63.

Leucocytosis in polycythaemia vera predicts both inferior survival and leukaemic transformation

Leucocytosis (leucocyte count >15 x 10(9)/l) was recently associated with thrombosis in polycythaemia vera (PV). This study sought the prognostic relevance of leucocytosis for survival and leukaemic or fibrotic transformation. Amongst 459 patients with PV seen at our institution in recent years (median age, 60 years; 56% males), 146 deaths and 88 leukaemic (n = 34) or fibrotic (n = 54) transformations were documented. Arterial or venous thrombosis occurred in 14% and 9% of patients at diagnosis and in 25% and 15% during follow-up, respectively. Multivariate analysis identified the advanced age (P < 0.0001), leucocytosis (leucocyte count >/=15 x 10(9)/l; P = 0.0006) and arterial thrombosis at diagnosis (P = 0.01) as independent predictors of inferior survival. In the absence of the first two risk factors, median survival was projected at 272 months as opposed to 108 months in the presence of both risk factors (P < 0.0001). Leucocytosis was also identified as an independent predictor of both leukaemic transformation and venous thrombosis during follow-up. Time-to-event analysis did not disclose a significant association between single or multiple cytotoxic drug exposure and either leukaemic or fibrotic transformation. The current study highlighted the prognostic relevance of leucocytosis on various aspects of the disease in PV.

Prospective identification of high-risk polycythemia vera patients based on JAK2(V617F) allele burden

The aim of this study was to determine whether the burden of JAK2(V617F) allele correlated with major clinical outcomes in patients with polycythemia vera (PV). To this end, we determined JAK2 mutant allele levels in granulocytes of 173 PV patients at diagnosis. The mean (+/-s.d.) mutant allele burden was 52% (+/-29); 32 patients (18%) had greater than 75% mutant allele. The burden of JAK2(V617F) allele correlated with measurements of stimulated erythropoiesis (higher hematocrit, lower mean cell volume, serum ferritin and erythropoietin levels) and myelopoiesis (higher white cell count, neutrophil count and serum lactate dehydrogenase) and with markers of neutrophil activation (elevated leukocyte alkaline phosphatase and PRV-1 expression). As compared to those with less than 25% mutant allele, patients harboring greater than 75% JAK2(V617F) allele were at higher relative risk (RR) of presenting larger spleen (RR 4.7; P<0.001) or suffering from pruritus (RR 3.1; P<0.001). In these patients, the risk of requiring chemotherapy (RR 1.8; P=0.001) or developing major cardiovascular events (RR 7.1; P=0.003) during follow up were significantly increased. We conclude that a burden of JAK2(V617F) allele greater than 75% at diagnosis points to PV patients with high-risk disease.

How I treat patients with polycythemia vera

The clinical course of polycythemia vera (PV) is marked by a high incidence of thrombotic complications; fibrotic and leukemic disease transformations are additional causes of morbidity and mortality. Major predictors of vascular events are increasing age and previous thrombosis; leukocytosis and high JAK2 V617F allele burden are currently being investigated for additional prognostic value in this regard. Myelosuppressive drugs can reduce the rate of thrombosis, but there is concern that their use raises the risk of transformation into acute leukemia. To tackle this dilemma, a risk-oriented management strategy is recommended. Low-risk patients should be treated with phlebotomy and low-dose aspirin. Cytotoxic therapy is indicated in high-risk patients, and the drug of choice is hydroxyurea because of its efficacy in preventing thrombosis and low leukemogenicity. Interferon-alpha should be reserved for selected categories of patients due to high cost and toxicity. The demonstration of JAK2 V617F mutation in the vast majority of PV patients opens the avenue for the development of promising new molecularly targeted drugs.