Basophilia in Polycythemia Vera Is Associated with an Increased Risk of Leukemic and Myelofibrotic Transformation

Background

Absolute basophil count (ABC) might be increased in patients with myeloproliferative neoplasms and has been associated with poor prognosis in chronic myeloid leukemia (CML) and, possibly, primary myelofibrosis (PMF, Front. Oncol 2019;9:872). In a Mayo Clinic survey of 382 patients with BCR::ABL1-negative leukocytosis and ABC ≥0.09 x 10⁹/L, 191 (50%) were associated with myeloid neoplasms, including 104 (27%) with CML, 23 (6%) essential thrombocythemia, 21 (6%) polycythemia vera (PV), and 18 (5%) PMF (AJH 2020;95:E216). Herein, we tapped into a well-characterized cohort of patients with PV, in order to describe the prevalence of basophilia, at specific ABC thresholds, and corresponding clinical, molecular, and prognostic correlates.

Methods

Study patients were retrospectively recruited from Mayo Clinic (USA) databases, after approval from IRB. Diagnostic criteria were according to the International Consensus Classification (Blood 2022;140:1200). Study inclusion criteria included the availability of information on ABC and absolute eosinophil count (AEC). Mayo Clinic institutional reference range for ABC was 0.01 to 0.08 x 10⁹/L and for AEC 0.03 to 0.48 x 10⁹/L. “Eosinophilia” was defined as an AEC of ≥0.6 x 10⁹/L. Basophilia was evaluated both at an ABC of ≥0.1 x 10⁹/L and ABC of ≥0.3 x 10⁹/L, the latter representing 3 x the upper limit of the normal reference range. Cytogenetic information obtained within one year of diagnosis was available in 270 patients. Next-generation sequencing information collected before disease transformation was available in 99 patients. Conventional statistical methods were employed for comparisons of groups and survival analysis (JMP Pro 17.0.0 software SAS Institute, Cary, NC, USA).

Results

Information on ABC and AEC, obtained within one year of diagnosis, was available in 478 patients (median age 66 years; males 51%). Median values at presentation were 10.6 x 10⁹/L for leukocyte count, 453 x 10⁹/L platelet count, and 17.3 g/dL hemoglobin level. Presenting symptoms included palpable splenomegaly 24%, pruritus 31%, arterial thrombosis 12%, and venous thrombosis 17%. Median and range values for ABC and AEC were 0.12 x 10⁹/L (0-3.2) and 0.27 x 10⁹/L (0-6.5), respectively. ABC was ≥0.3 x 10⁹/L in 80 (17%) patients and ≥0.1 x 10⁹/L in 315 (66%). AEC was ≥0.6 x 10⁹/L in 68 (14.6%) patients. ABC≥0.3 x 10⁹/L was associated with AEC ≥0.6 x 10⁹/L (p<0.01), leukocytosis (p<0.01), and palpable splenomegaly (p=0.02), but not platelet count, pruritus, smoking history, diabetes, or arterial or venous thrombosis; in multivariable analysis, the association with leukocytosis, but not that with splenomegaly, was confirmed.

At a median follow-up of 5.7 years (range 0.03-32.8), 132 (28%) deaths, 17 (3.6%) leukemic and 40 (8.4%) fibrotic progressions were documented. Post-diagnosis events also included arterial (7%) and venous (9%) thrombosis. In univariate analysis, neither ABC (p=0.8, 0.7, and 0.96) nor AEC (p=0.7, 0.6, and 0.8), evaluated as continuous variables, affected overall (OS), leukemia-free (LFS), or myelofibrosis-free (MFFS) survival, respectively. Similarly, eosinophilia at AEC ≥0.6 x 10⁹/L did not appear to influence OS (p=0.99), LFS (p=0.6) or MFFS (p=0.5). On the other hand, although basophilia at ABC≥0.3 x 10⁹/L did not affect OS (p=0.27), it was significantly associated with inferior LFS (HR 6.5, 95% CI 2.3-18.0; p<0.01) and MFFS (HR 2.3, 95% CI 1.2-4.5; p=0.01); the corresponding p values for ABC≥0.1 x 10⁹/L were 0.7, 0.1, and 0.17. The detrimental impact of basophilia (ABC≥0.3 x 10⁹/L) on LFS was confirmed (P<0.01) with multivariable analysis that included other clinical variables, including leukocytosis (NS), platelet count (NS), basophil percentage (NS), age (p<0.01), and palpable splenomegaly (p<0.01). Results were similar during multivariable analysis for MFFS with palpable splenomegaly (p<0.01), ABC≥0.3 x 10⁹/L (p=0.03), and age (p=0.05) sustaining independent predictive value. The number of informative cases was too small to evaluate prognostic interaction with mutations and karyotype.

Conclusions:

Basophilia in PV is associated with palpable splenomegaly and leukocytosis and independently predicts leukemic and myelofibrotic transformation. Additional studies are needed to confirm these observations and examine prognostic interaction with mutations and karyotype.

Begna:Novartis: Membership on an entity's Board of Directors or advisory committees. Gangat:DISC Medicine: Consultancy, Other: Advisory Board ; Agios: Other: Advisory Board.