The Mutational Landscape of Polycythemia Vera and Its Phenotypic and Prognostic Correlates

Background:

JAK2 mutations are invariably associated with polycythemia vera (PV); more than 50% of affected patients also harbor non-JAK2 mutations, some considered prognostically relevant (BJH 2020;189:291). We queried a large single institutional database of patients with PV, in order to examine the incidence and distribution of non-JAK2 mutations, across different disease stages, in order to assess their impact on disease phenotype and prognosis, in the context of other risk factors.

Methods:

Mayo Clinic databases (1998-2023) were searched to identify next-generation sequencing (NGS)-annotated patients with PV, with diagnosis retrospectively fitted to meet the 2022 International Consensus Classification (ICC) criteria (Blood 2022; 140:1200). NGS was performed either through research-based targeted capture assays or a clinically ordered 42-gene panel. Conventional statistical methods were used for group comparisons and survival analyses.

Results:

i) Mutational frequencies in chronic vs. transformed disease phases

319 patients with PV were considered; NGS was performed at time of i) diagnosis or before fibrotic or leukemic transformation (N=270; 84.6%), ii) fibrotic progression (N=37; 11.6%), or iii) leukemic transformation (N=12; 3.8%). Mutational frequencies in newly-diagnosed/chronic phase PV were 19% for TET2, 10% for ASXL1, 4% for SRSF2, ⁓3% each for SF3B1, DNMT3A, and SH2B3, and 1-2% each for TP53 and IDH2. Significant differences in mutation distribution were apparent for TP53/SRSF2/IDH1/U2AF1 in blast (50%/25%/17%/8%) vs. fibrotic (8%/0%/0%/5%) vs. chronic (2%/4%/2%/0.4%) phase (p<0.01, <0.01, =0.03, and =0.03, respectively).

ii) Phenotypic correlates of specific mutations among patients with NGS information obtained during chronic phase (N=270)

Median age was 61.4 years (51% males) and incidence rates included 22% for leukocytosis ( ≥15 x 10(9)/L) and 25%/14% for arterial/venous thrombosis history. Numerically prevalent or prognostically relevant mutations were selected for comparison of clinical or laboratory characteristics: TET2, ASXL1, SRSF2, TP53, IDH2. Significant associations were apparent for ASXL1 (younger age distribution), SRSF2 (older age distribution, leukocytosis), and TP53 (leukocytosis) mutations. Median age was 66.4, 58.7, 76.8, 63.9, and 68.6 years for TET2, ASXL1, SRSF2, TP53, IDH2 mutations, respectively (p<0.01). The corresponding median leukocyte counts were 12.1, 11.4, 14.4, 16.7, and 11.5 x 10(9)/L (p<0.01).

iii) Prognostic impact of mutations detected at diagnosis or chronic phase (N=270)

At median follow-up of 9.5 years (range 0.1-42.4), 115 (43%) deaths, 12 (4%) leukemic transformations, and 53 (20%) fibrotic progressions were documented. In univariate analysis of mutations, overall survival (OS) was adversely affected by SRSF2 and IDH2 mutations, leukemia-free survival (LFS) by ASXL1, SRSF2, IDH2, RUNX1, and CEBPA mutations, and myelofibrosis-free survival (MFS) by SRSF2 mutation. Age-adjusted (p<0.01) multivariable analysis, including mutations and other risk variables, identified SRSF2 (HR 4.2, 95% CI 1.9-9.5), ASXL1 (HR 2.0, 1.1-3.7), IDH2 (HR 5.3, 1.8-15.3) mutations and leukocytosis ≥15 x 10(9)/L (HR 2.0, 1.3-3.1) as independent predictors of inferior OS. SRSF2 and ASXL1 mutations were also independently associated with inferior LFS (p=0.02 and 0.06, respectively) and SRSF2 (p<0.01) and karyotype (p<0.01) with inferior MFS (p<0.01). Median survival for 235 patients without any adverse mutation (ASXL1, SRSF2, or IDH2) was 17.8 years vs. 8.8 years for 35 patients with any one of the three adverse mutations (p=0.01; HR 1.8, 95% CI 1.1-2.9). The number of non-JAK2 mutations, in general, was also associated with significantly different survival outcomes: median OS was 20, 15.1, and 9.3 years for patients with non-JAK2 mutations numbering zero, one, or two or more, respectively (p<0.01)

Conclusions:

SRSF2 mutations in PV cluster with older and ASXL1 with younger age distribution. SRSF2 and TP53 mutational frequencies were higher in blast-phase disease. SRSF2, ASXL1, and IDH2 mutations were significantly associated with inferior OS, independent of each other and other risk factors. SRSF2 mutations were also detrimental to LFS and MFS and ASXL1 to LFS. Such information might allow further refinement of current risk models for PV, which in future studies should also account for variant allele frequency.