Initial bone marrow reticulin fibrosis in polycythemia vera exerts an impact on clinical outcome

We examined the prevalence and prognostic relevance of bone marrow reticulin fibrosis in 526 patients with WHO-defined polycythemia vera (PV) evaluated at time of initial diagnosis. Seventy-four (14%) patients displayed mostly grade-1 reticulin fibrosis with only 2 cases showing higher grade fibrosis. Presenting clinical and laboratory characteristics, including JAK2V617F allele burden, between patients with and without fibrosis were mostly similar with the exception of a higher prevalence of palpable splenomegaly in patients with fibrosis (p<0.01). Patients with fibrosis were less prone to experience thrombosis during their clinical course (1.1 vs. 2.7/100 patient-years; p=0.03) and more prone to develop post-PV myelofibrosis (2.2 vs. 0.8/100 patient-years; p=0.01). There was no significant difference between the two groups in terms of overall or leukemia-free survival. The current study clarifies the incidence, degree, and prognostic relevance of bone marrow fibrosis obtained at time of initial diagnosis of PV.