Significance of thrombocytopenia in patients with primary and postessential thrombocythemia/polycythemia vera myelofibrosis

Severe thrombocytopenia (platelets <50 × 10⁹/L) is associated with very poor outcome of patients with myelofibrosis (MF). As patients with primary myelofibrosis (PMF) differ from patients with postessential thrombocythemia (PET-MF) and postpolycythemia vera myelofibrosis (PPV-MF), we aimed to evaluate the significance of low platelets among these patients. We present clinical characteristics and outcome of patients with either PMF, PPV-MF, or PET-MF, and thrombocytopenia who presented to our institution between 1984 and 2015. Of 1269 patients (877 PMF, 212 PPV-MF, 180 PET-MF), 11% and 14% had platelets either <50 × 10⁹/L or between 50-100 × 10⁹/L, respectively. Patients with platelets <50 × 10⁹/L were most anemic and transfusion dependent, had highest blast count and unfavorable karyotype. In general, their overall and leukemia-free survival was the shortest with median time of 15 and 13 months, respectively; with incidence of acute leukemia almost twice as high as in the remaining patients (6.9 vs 3.6 cases per 100 person-years). Nevertheless, this observation remains mostly significant for patients with PMF, as those with PEV/PVT-MF have already significantly inferior prognosis with platelets <100 × 10⁹/L.