Granulocyte MPL-mutant allele burden according to the degree of bone marrow fibrosis in patients with myeloproliferative neoplasms. Data are shown in a box plot depicting the lower and upper adjacent values (lowest and highest horizontal line, respectively) and lower and upper quartile with median value (box). (Upper panel, A) The proportion of MPL-mutant alleles was significantly higher in patients with bone marrow fibrosis than in those without bone marrow fibrosis (P < .0001). (Lower panel, B) The relationship also remained statistically significant (P = .0001) when categorizing patients according to grade of fibrosis (grade 0 vs grade 1 vs grade 2 to 3), defined according to the European consensus criteria.²⁵