European vs 2015-World Health Organization clinical molecular and pathological classification of myeloproliferative neoplasms

Table 9 2015 WHO Clinical Molecular and Pathological criteria for the diagnosis of normocelular essential thrombocythemia carrying one of the MPL⁵¹⁵ mutations[78]

CM JAK2 wild type ET	Bone marrow pathology (P) criteria (WHO)
(1) Platelet count > 350 × 109/L and presence of large platelets in blood smear	P1 Proliferation of large to giant mature megakaryocyte with hyperlobulated, staghorn-like nuclei in a normocellular bone marrow (< 65%)
(2) Hemoglobin, haematocrit and erythrocyte count in the normal range	No increase of erythropoiesis, and no increase or immaturity of granulopoiesis or erythropoiesis, no or slight increase in reticulin RF 0/1
(3) Presence of MPL515 mutation and JAK2 wild type	ET → MF
(4) Normal serum EPO	Increased reticulin fibrosis around dense clustered megakaryocytes in a normocellular bone marrow and reduced erythropoiesis. Follow-up data of RF and MF related to splenomegaly in MPL515 ET transltional states to MF are lacking. Grading of RF and MF similar as described for PV
(5) Normal LAP score and CD11b expression
(6) No or slight splenomegaly
(7) No leukoerythroblastosis
(8) No preceding or allied CML, PV, RAS-T or MDS

This entity is identical to “true” ET as defined in 2002 by Michiels and Thiele in Table 5[91]. ET: Essential thrombocythemia; CM: Clinical and molecular; RF: Reticulin fibrosis; MF: Myelofibrosis; EPO: Erythropoetin; LAP: Leukocyte alkaline phosphatase; CML: Chronic myeloid leukemia; PV: Polycythemia vera; MDS: Myelodysplatic syndrome; WHO: World Health Organization.