Aim To characterise the clinical and histological features of MPL-mutated essential thrombocythaemia (ET).
Patients and methods Bone marrow biopsies of 175 patients with ET were centrally reviewed according to the 2016 WHO classification, including 42 cases with MPL mutation, 98 JAK2V617F-mutated and 35 CALR-mutated. Clinical and histological features were compared among the three genotypes included in the current 2016 WHO classification and among the different types of MPL mutations.
Results Patients with MPL-mutated ET were significantly older than those with the other genotypes. Haematological values at diagnosis were similar among MPL-mutated and CALR-mutated ET, with both genotypes showing higher platelet counts and lower haemoglobin values than ET with JAK2V617F genotype. In the bone marrow, the median number of megakaryocytes was higher in MPL and CALR than in JAK2V617F genotype (16, 19 and 14 megakaryocytes per ×20 power field, respectively, p=0.004). Histological features of prefibrotic myelofibrosis were rarely observed in MPL genotype, whereas sinusoidal hyperplasia, dense clusters of megakaryocytes and reticulin fibrosis were more frequent in CALR-mutated ET, with 11% of such cases fulfilling WHO 2016 histological criteria of prefibrotic myelofibrosis. With a median follow-up of 3.5 years, no significant differences were seen among genotypes regarding survival, vascular complications or myelofibrotic transformation. There were no significant differences in the clinical data or in the histological characteristics depending on the type of MPL mutation.
Conclusion MPL and CALR ET genotypes share clinical and histological characteristics. In contrast to CALR genotype, features of prefibrotic myelofibrosis are uncommon in MPL-mutated ET.
- essential thrombocythemia
- diagnostic hematology
- myeloproliferative neoplasms
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Handling editor Mary Frances McMullin.
Contributors AA-L designed the study, collected the data, performed the statistical analysis, analysed and interpreted the results, and wrote the paper. DM, LA, LC and MR reviewed the bone marrow biopsies, interpreted the results and wrote the paper. AR collected the data, performed statistical analysis and approved the final version. NP reviewed the bone marrow biopsies and approved the final version. EA-R, JoMA, SN, GC-T, FF-M, MAD, MP-E, JuMA, MIM, EM, CM and IP-G collected the data and approved the final version. ML-G performed the molecular studies and approved the final version. JCHB, FC and CB collected the data, interpreted the results and wrote the paper.
Funding This work was supported by grants from the Instituto de Salud Carlos III (PI13/00557, PI13/0636, PI1300393 and RD12/0036/0010).
Competing interests None declared.
Patient consent Not required.
Ethics approval Hospital del MAR IRB.
Provenance and peer review Not commissioned; externally peer reviewed.