Monocytosis in Polycythemia Vera: Clinical and Molecular Correlates

Background

Polycythemia Vera (PV) constitutes one of the three BCR-ABL1-negative myeloproliferative neoplasms and is characterized by clonal erythrocytosis and the almost invariable presence of JAK2 mutation. An absolute monocyte count (AMC) of ≥1 x 10(9)/L defines chronic myelomonocytic leukemia (CMML) but can also be seen in other myeloid disorders including myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN). The presence or development of monocytosis has previously been shown to confer poor prognosis in both primary myelofibrosis (PMF), which is one of the three BCR-ABL1-negative MPN (Leukemia Research 2007;31:1503, Mod Pathol. 2013 Feb;26(2):204) and MDS (Haematologica. 1997;82:25). In the current study, we examined the clinical, prognostic and molecular correlates of monocytosis in PV.

Methods

Study patients were selected from our institutional database of MPN and fulfilled the 2008 World Health Organization (WHO) criteria for the diagnosis of PV (Blood. 2009;114:937). Cytogenetic and mutational analyses were performed according to conventional methods (Leukemia. 2014;28:2206) any assignment as unfavorable karyotype was per PMF criteria (Leukemia. 2011;25:82). Mutation screening included TET2, ASXL1 and SRSF2 because of their known association with CMML (Leukemia. 2014;28:2206) Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis.

Results

Patient characteristics:

Analysis was conducted on 587 patients (median age 60 years; 48% males) who met WHO criteria for diagnosis of PV. Amongst them, accurate documentation of AMC was available in 237 patients, cytogenetic information in 239, and ASXL1, TET2 and SRSF2 mutational status in 133 patients. Median (range) values were for AMC 0.6 x 10(9)/L (0-4.7) and leukocytes 11.6 x 10(9)/L (3.8-171.6). 31% of 506 informative patients had palpable splenomegaly, 34% of 551 had microcirculatory symptoms, 30% of 566 had pruritus, 8% of 504 had erythromelalgia, 42% of 581 had hypertension, 9% of 584 had diabetes and 11% of 575 were active tobacco users. 25% of the patients presented with history of thrombosis and 22% developed thrombosis after diagnosis. Cytogenetic findings were abnormal in 19%, of whom 20% were unfavorable. TET2, ASXL1 and SRSF2 mutations were documented in 18%, 11% and 3%, respectively. During follow-up, 224 (38%) patients died and median follow-up for living patients was 109 months. Median survival was 16 years and leukemic or fibrotic transformations were documented in 4% and 14%, respectively.

Comparison of patients with and without monocytosis:

Among 237 informative patients, 32 (14%) displayed monocytosis (AMC ≥1 x 10(9)/L) at time of diagnosis. PV patients with monocytosis were older (p=0.006) and displayed higher leukocyte count (p<0.0001) and higher incidences of leukocytosis (p=0.024) and unfavorable cytogenetic abnormalities (p=0.02). There was no association between monocytosis and mutations for TET2 (p=0.1), ASXL1 (p=0.7) and SRSF2 (p=0.3) or thrombosis before (p=0.9) or after (p=0.5) diagnosis (p=0.5), palpable splenomegaly (p=0.6), pruritus (p=0.7) or microcirculatory symptoms (p=0.1).

Among the 237 PV patients in whom information regarding AMC was available, 70 (30%) died during follow-up and 49 (21%), 23 (10%), 9 (4%) developed thrombosis, leukemic transformation or fibrotic progression, respectively. In univariate analysis, overall (p=0.009; HR 2.0, 95% CI 1.2-3.4) but not leukemia-free (p=0.79), myelofibrosis-free (p=0.13) or thrombosis-free (p=0.48) survivals were different between patients with or without monocytosis. Furthermore, the significant difference in survival was no longer apparent when analysis was adjusted for age (p=0.13), unfavorable karyotype (0.17) or leukocytosis (p=0.06).

Conclusions

Monocytosis (AMC ≥1 x 10(9)/L) is not infrequent in PV (14%). However, the presence of monocytosis does not appear to represent a significantly different phenotype in terms of molecular characteristics although it is associated with older age, leukocytosis and unfavorable karyotype. The latter associations account for the inferior survival seen in patients with monocytosis.