Granulocyte MPL-mutant allele burden according to mutation type 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). The median allele burden was 32.9% in the MPL (W515L) group (39 patients), 56.2% in the MPL (W515K) group (11 patients), and 49.9% in the MPL (W515A) group (7 patients), with no significant difference between subgroups (W515L vs W515K P = .186; W515L vs W515A P = .079; and W515K vs W515A P = .821). When restricting the analysis to patients with ET, we found a significant difference among the 3 subgroups (P = .014). The median allele burden was 18.2% in the MPL (W515L) group (22 patients), 41.3% in the MPL (W515K) group (7 patients), and 51.1% in the MPL (W515A) group (6 patients) (W515L vs W515K P = .103; W515L vs W515A P = .0051; W515K vs W515A P = .568).