Unifying Concepts

WHO Diagnostic Criteria for Prefibrotic or Early-Stage Myelofibrosis (pre-PMF)

Prefibrotic myelofibrosis (pre-PMF) is a distinct entity among chronic myeloproliferative neoplasm diagnosed according to the revised WHO classification. The clinical picture is heterogeneous, ranging from isolated thrombocytosis, mimicking essential thrombocythemia (ET), to symptoms of high-risk PMF.

WHO Diagnostic Criteria for Prefibrotic or Early-Stage Myelofibrosis

Diagnosis requires all major criteria and at least one minor criterion.

Major criteria

  • Megakaryocytic proliferation and atypia, without reticulin fibrosis > grade 1, accompanied by increased, age-adjusted bone marrow cellularity, granulocytic proliferation, and in many cases decreased erythropoiesis
  • Criteria for BCR-ABL1-positive chronic myeloid leukemia, polycythemia vera, essential thrombocythemia, myelodysplastic syndrome, or other myeloid neoplasm not met
  • JAK2 V617F, CALR, or MPL mutation or presence of another clonal marker or of minor reactive reticulin fibrosis in bone marrow†

Minor criteria

  • Anemia not attributed to a coexisting condition
  • Leukocytosis (≥11,000 cells per cubic millimeter)
  • Palpable splenomegaly
  • Lactate dehydrogenase level above upper limit of normal of institutional reference range

† In the absence of any of the three major clonal mutations, a search for other mutations associated with myeloid neoplasms (e.g., ASXL1, EZH2, TET2, IDH1, IDH12, SRSF2, and SF3B1 mutations) may be helpful in determining the clonal nature of the disease. Minor (grade 1) reticulin fibrosis caused by infection is noteworthy, as are autoimmune disorders or other chronic inflammatory conditions, hairy-cell leukemia or other lymphoid neoplasms, metastatic cancer, or toxic (i.e., chronic) myelopathies.



  1. Finazzi G, Vannucchi AM, Barbui T. Prefibrotic myelofibrosis: treatment algorithm 2018. Blood Cancer J. 2018;8(11):104. [Medline]
  2. Rumi E, Sant’Antonio E, Boveri E, et al. Diagnosis and management of prefibrotic myelofibrosis. Expert Rev Hematol. 2018;11(7):537–545. [Medline]
  3. Tefferi A, Pardanani A. Essential Thrombocythemia. N Engl J Med. 2019;381(22):2135–2144. [Medline]


Created Dec 23, 2019.

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