Basophilia and eosinophilia in polycythemia vera and essential thrombocythemia: clinical, genotype, and prognostic correlates.

The current retrospective study evaluated clinical, genetic, and prognostic correlates of increased absolute basophil (ABC) and eosinophil (AEC) counts in polycythemia vera (PV; N = 475) and essential thrombocythemia (ET; N = 658). Median (range) ABC and AEC were 0.1 (0-3.2) and 0.3 (0-6.5) x 109/L in PV and 0.07 (0-0.8) and 0.2 (0-1.4) x 109/L in ET. In PV, ABC ≥ 0.1 × 10⁹/L was associated with palpable splenomegaly and increased AEC, leukocyte count, and platelet count while AEC ≥ 0.5 × 10⁹/L was associated with increased ABC and leukocyte count. In ET, ABC ≥ 0.1 × 10⁹/L was associated with increased AEC, leukocyte count, platelet count, and cardiovascular risk factors while AEC ≥ 0.5 × 10⁹/L correlated with ABC and increased leukocyte count; genetic associations were seen only in ET and included ABC ≥ 0.1 × 10⁹/L with triple-negative driver mutation status (p = 0.03). In PV, AEC did not correlate with overall (OS), leukemia-free (LFS), myelofibrosis-free (MFFS), arterial thrombosis-free (ATFS), or venous thrombosis-free (VTFS) survival; by contrast, ABC ≥ 0.1 × 10⁹/L was associated with longer ATFS (p = 0.03) while ABC ≥ 0.3 × 10⁹/L was associated with inferior LFS (p < 0.01) and MFFS (p < 0.01); the associations with LFS and MFFS were sustained during multivariable analysis. In ET, both ABC ≥ 0.1 × 10⁹/L and AEC ≥ 0.5 × 10⁹/L were independently associated with inferior OS but impact on LFS, MFFS, ATFS, or VTFS was not apparent. The results from the current study warrant additional studies to clarify the potential association between basophilia in PV and disease transformation into acute myeloid leukemia and myelofibrosis.