Classification of MF

Establishing an accurate myelofibrosis (MF) diagnosis and classification is important, as it impacts risk stratification and clinical decision makingNg ZY et al. Int J Lab Hematol. 2023;45(suppl 2):59-70. Thiele J et al. Blood Cancer J. 2025;15(1):31.

• Two updated classifications for ET, PV, primary MF (PMF), and secondary MF (post-ET and post-PV MF) were developed in 2022: the World Health Organization 5th edition classification (WHO5) and the International Consensus Classification (ICC) of myeloid neoplasms and acute leukemiaKhoury JD et al. Leukemia. 2022;36:1703-1719. Arber DA et al. Blood. 2022;140(11):1200-1228.
• The 2 classifications are similar, integrating morphologic features, molecular/genetic data, clinical and laboratory parameters, and the exclusion of other myeloproliferative neoplasms (MPNs)Thiele J et al. Blood Cancer J. 2025;15(1):31. Arber DA et al. Blood. 2022;140(11):1200-1228. Shao R et al. Cancers (Basel). 2025;18(1):50.

Overview of WHO5 and ICC MF classificationThiele J et al. Blood Cancer J. 2025;15(1):31. Arber DA et al. Blood. 2022;140(11):1200-1228. Shao R et al. Cancers (Basel). 2025;18(1):50. Garmezy B et al. Blood Rev. 2021;45:100691.

Continue reading for the complete diagnostic criteria of overt, fibrotic PMF, post-ET MF, and post-PV MF.

CBC, complete blood count; ET, essential thrombocythemia; ICC, International Consensus Classification; MPN, myeloproliferative neoplasm; PMF, primary myelofibrosis; PV, polycythemia vera; WHO5, World Health Organization 5th edition classification.

PMF classification according to WHO5 and ICCThiele J et al. Blood Cancer J. 2025;15(1):31.

• In both WHO5 and ICC classifications, PMF is broken into an early/prefibrotic stage (pre-PMF) and an overt, fibrotic stage (fibrotic PMF)Thiele J et al. Blood Cancer J. 2025;15(1):31.
  
  
  • The key distinguishing criterion is fibrosis grade; bone marrow fibrosis grades 2-3 define fibrotic PMF, while grades 0-1 define pre-PMFThiele J et al. Blood Cancer J. 2025;15(1):31.
    
  • Fibrotic PMF more commonly presents with leukoerythroblastosis, which is included among its minor criteriaThiele J et al. Blood Cancer J. 2025;15(1):31.
• WHO5 and ICC classifications include the same major and minor criteria for fibrotic PMF and require all 3 major criteria and at least 1 minor criterion for diagnosisThiele J et al. Blood Cancer J. 2025;15(1):31.

Combined WHO5 and ICC diagnostic criteria for overt, fibrotic stage PMFThiele J et al. Blood Cancer J. 2025;15(1):31.

Diagnosis requires all 3 major criteria and at least 1 minor criterion confirmed in 2 consecutive assessments.

Adapted from Blood Cancer J.Thiele J et al. Blood Cancer J. 2025;15(1):31.

CML, chronic myelogenous leukemia; ET, essential thrombocythemia; ICC, International Consensus Classification; LDH, lactate dehydrogenase; MDS, myelodysplastic syndromes; PMF, primary myelofibrosis; PV, polycythemia vera; WHO5, World Health Organization 5th edition classification.

Secondary MF classification according to ICCArber DA et al. Blood. 2022;140(11):1200-1228.

• In the ICC classification, secondary MF is broken into post-ET and post-PV MFArber DA et al. Blood. 2022;140(11):1200-1228.
  
  
  • The primary criterion for post-ET and post-PV MF is prior documentation of ET or PV, and bone marrow fibrosis grade ≥2Arber DA et al. Blood. 2022;140(11):1200-1228.
  • The 2 types of secondary MF have distinct additional criteria, of which at least 2 must be present; the key distinguishing criterion is inclusion of elevated LDH for post-ET MFArber DA et al. Blood. 2022;140(11):1200-1228.

ICC diagnostic criteria for secondary MFArber DA et al. Blood. 2022;140(11):1200-1228. Tefferi A. Am J Hematol. 2023;98(5):801-821.

Adapted from Am J Hematol.Arber DA et al. Blood. 2022;140(11):1200-1228.

^aDiffuse often coarse fiber network with or without evidence of collagenization (trichrome stain).

^bDevelopment of any 2 (or all 3) of the following constitutional symptoms: >10% weight loss in 6 months, night sweats, unexplained fever (>37.5°C).

ET, essential thrombocythemia; Hb, hemoglobin; ICC, International Consensus Classification; IWG-MRT, International Working Group-Myeloproliferative Neoplasms Research and Treatment; LDH, lactate dehydrogenase; MF, myelofibrosis; PV, polycythemia vera.