Granulocyte MPL-mutant allele burden in patients with different myeloproliferative neoplasms. Data are shown in a box plot depicting the lower and upper adjacent values (lowest and highest horizontal line, respectively), lower and upper quartile with median value (box), and outside values (dots). The Kruskal-Wallis test showed a different distribution among different MPN subtypes (P = .0031). The median allele burden was significantly lower in ET compared with PMF (32.8% vs 59.4%; P = .0037) or post-ET myelofibrosis (post-ET MF; 32.8% vs 58.2%; P = .02), but there was no difference between PMF and post-ET myelofibrosis.