JAK2V617F Mutational Load in Patients with Polycythemia Vera (PV) Measured by Peripheral Blood DNA Is Associated with Disease Severity.

Abstract

Different methods using peripheral blood RNA (Vannucchi AM, et al. Leukemia . 2007,1–8), or archival bone marrow DNA (Tefferi A, et al. Leukemia . 2007,1–2) have yielded varied results correlating allele burden with severity and duration of disease. We therefore aimed to determine whether JAK2V617F allele burden correlated with certain parameters of disease. At our institution, 105 patients were diagnosed according to the criteria of the Polycythemia Vera Study Group. We grouped their JAK2V617F allele burdens into quintiles. DNA from peripheral blood was analyzed using pyrosequencing. For those patients whose allele burden was <5%, a sensitive ARMS (amplification refractory mutation system) assay was performed to demonstrate the presence of the JAK2V617F allele. Duration of disease was assessed from onset of symptoms. Spleen size was measured in cm below the midpoint of the left costal margin in the midclavicular line and categorized as not enlarged, slightly (1–3 cm), moderately (4–9 cm), or grossly enlarged (>9 cm). Thrombotic events were recorded within 5 years of JAK2V617F determination. There were 52 men and 53 women. The patients ranged in age from 35 to 88 years, median 60 years. The median duration of disease was 7.4 years (range: 0.2 - 36.6 years), and the median duration of follow-up after JAK2V617F determination was 12 months year (range: 1 - 43 months). The mean mutant allele burden was 46.0% (s.d. ± 29.7%). The fifth, and highest quintile had a mean mutant allele burden of 90.2% (s.d. ± 5.8%); the lowest quintile had a mean mutant allele burden of 9.9% (s.d. ± 6.3%). JAK2V617F did not correlate with age, gender, hematocrit and platelet count at diagnosis, or rate of phlebotomy prior to cytoreductive therapy. Increasing JAK2V617F burden did correlate with higher WBC at diagnosis (P=0.02), degree of splenomegaly (P<0.0001), presence of marrow fibrosis (P=0.03), and longer duration of disease (P=0.001). There was a trend for a higher JAK2V617F allele burden among patients with venous compared to arterial thrombosis. When the subset of patients who had JAK2V617F testing performed within 5 years of diagnosis (N=35) was examined, trends similar to those we had reported for all 105 patients were found, but no definitive statement can be made because of the small sample size. We noted a JAK2V617F allele burden of more than 80% during the course of the illness was associated with a significant disease phenotype. This is the first report of increased marrow fibrosis associated with high JAK2V617F burden. The importance of using quantitative JAK2V617F for assessing allele burden is stressed because patients with an increased allele burden may be candidates for anti-JAK therapy.