Thrombocytosis Phenotype in Prefibrotic Primary Myelofibrosis: Risk Stratification and Prognostic Significance

Essential thrombocythemia, prefibrotic primary myelofibrosis (pre-PMF), and overt primary myelofibrosis are myeloproliferative neoplasms with overlapping clinical features but different prognoses. We investigated the prognostic impact of thrombocytosis in pre-PMF.

This retrospective study analyzed patients diagnosed with myeloproliferative neoplasms at Taipei Veterans General Hospital from 2002 to 2023. Diagnoses were assigned by integrated clinicopathologic review using World Health Organization criteria. Overall survival was analyzed using Cox proportional hazards models. For complication endpoint, including leukemic transformation, thrombosis, and bleeding, competing-risk methods were used, with death treated as a competing event.

Among 350 patients with myeloproliferative neoplasms, the median age was 68 years, and 60.3% were male. Compared with pre-PMF patients without thrombocytosis, essential thrombocythemia did not have a significantly different risk of death (hazard ratio [HR] 0.77, 95% confidence interval [CI] 0.30-1.97; P = .586), whereas overt primary myelofibrosis had a significantly higher risk of death (HR 2.80, 95% CI 1.10-7.10; P = .030). In pre-PMF, thrombocytosis had a higher risk of death (HR 4.33, 95% CI 1.03-18.12; P = .045). Prognostic factors for worse survival in pre-PMF included constitutional symptoms (adjusted HR 10.81, 95% CI 2.63-44.36, P = .001), leukocytosis (adjusted HR 7.69, 95% CI 1.94-30.54, P = .004), and thrombocytosis (adjusted HR 7.80, 95% CI 1.49-40.82, P = .015).

Thrombocytosis was associated with inferior overall survival in pre-PMF. These findings support platelet count as a pragmatic risk stratifier in pre-PMF and highlight the clinical relevance of distinguishing pre-PMF from essential thrombocythemia and overt primary myelofibrosis.