Concomitant and noncanonical JAK2 and MPL mutations in JAK2V617F‐ and MPLW515 L‐positive myelofibrosis

Sequential genotyping for phenotype‐driver mutations in JAK2 (exon 14), CALR (exon 9), and MPL (exon 10) is recommended in patients with myeloproliferative neoplasms. Yet, atypical JAK2‐ and MPL‐mutations were described in some triple‐negative patients. Whether noncanonical and/or concomitant JAK2‐ and MPL‐mutations exist in myelofibrosis (MF) regardless of phenotype‐driver mutations is not yet elucidated. For this, next‐generation sequencing (NGS) was performed using blood genomic DNA from 128 MF patients (primary MF, n = 93; post‐ET–MF, n = 18; post‐PV–MF, n = 17). While no atypical JAK2‐ or MPL‐mutations were seen in 24 CALR‐positive samples, two JAK2‐mutations [c.3323A > G, p.N1108S; c.3188G > A, p.R1063H] were detected in two of the 21 (9.5%) triple‐negative patients. Twelve of the 82 (14.6%) JAK2V617F‐positive cases had coexisting germline JAK2‐mutations [JAK2R1063H, n = 6; JAK2R893T, n = 1; JAK2T525A, n = 1] or at least one somatic MPL‐mutation [MPLY591D, n = 3; MPLW515 L, n = 2; MPLE335K, n = 1]. Overall, MPL‐mutations always coexisted with JAK2V617F and/or other MPL‐mutations. None of the JAK2V617F plus a second JAK2‐mutation carried a TET2‐mutation but all patients with JAK2V617F plus an MPL‐mutation harbored a somatic TET2‐mutation. Four genomic clusters could be identified in the JAK2V617F‐positive cohort. Cluster‐I (10%) (noncanonical JAK2_{mutated (mut)} + TET2_{wildtype (wt)}) were younger and had less proliferative disease compared with cluster‐IV (5%) (TET2_mut + MPL_mut). In conclusion, recurrent concomitant classical and/or noncanonical JAK2‐ and MPL‐mutations could be detected by NGS in 15.7% of JAK2V617F‐ and MPLW515‐positive MF patients with genotype‐phenotype associations. Many of the germline and/or somatic mutations might act as “Significantly Mutated Genes” contributing to the pathogenesis and phenotypic heterogeneity. A cost‐effective NGS‐based approach might be an important step towards patient‐tailored medicine.