Surgical Pathology Criteria

Primary Myelofibrosis

Differential Diagnosis

Common Myeloproliferative Neoplasms - Overview

Tyrosine kinase ABL JAK2 JAK2 or MPL JAK2 or MPL
Blood ↑WBC with IG, basophils Normo or hypochromatic anemia, may have ↑platelets & basophils Leukoerythroblastic with teardrops ↑Platelets, often abnormal
Marrow ↑↑Myeloids Panmyelosis, ± erythroid hyperplasia, atypical megas Panmyelosis, atypical megas ↑↑Megas
Marrow fibrosis Varies ↑In spent phase ↑↑In fibrotic phase Minimal
Splenomegaly ++ ++ +++ ±
Clinical Presentation /Other B symptoms Hypertension, thrombosis, pruritus,↓EPO B symptoms, bleeding, gout Thrombosis, hemorrhage
CML = chronic myeloid leukemia; PV = polycythemia vera; PMF = primary myelofibrosis; ET = essential thrombocythemia; IG = immature granulocytes; Megas = megakaryocytes; EPO = erythropoietin

Essential Thrombocythemia vs Cellular Phase Primary Myelofibrosis vs CML

  Essential Thrombocythemia Cellular Phase Primary Myelofibrosis CML with p230
Cellularity Normal to moderately hypercellular Markedly hypercellular (cellular phase) Markedly hypercellular
Megas - Distribution Dispersed or loose clusters Tight clusters, touching each other Dispersed or loose clusters
Megas - Size Large and giant Pleomorphic Variable, may have dwarf forms
Megas - Nuclei Lobulated Bulbous, hyperchromatic Hypolobated
Megas - Cytoplasm Mature Variable, may have naked nuclei Mature
Granulopoietic Hyperplasia Infrequent, mild Moderate to marked in cellular phase Marked
Splenomegaly Infrequent Frequent Rare
JAK2V617I Allele burden <50% Allele burden >50%  
Megas = megakaryocytes

Hematolymphoid Disorders with Marrow Fibrosis (overview)

Disorder Distinguishing Feature(s)
Polycythemia Vera, Fibrotic Phase History of PV / JAK2+
Essential Thrombocythemia, Fibrotic Phase (rare) History of ET / may be JAK2+
CML, Fibrotic Phase History of CML / BCR-ABL1+
MDS with Fibrosis Dysplastic features in marrow
Acute Megakaryoblastic Leukemia Blasts, acute onset
Osteosclerotic Myeloma Plasma cells. light chain restricted
Acute Pan-myelosis with Myelofibrosis Bone pain, acute onset
Primary Myelofibrosis Clustered atypical megakaryocytic hyperplasia
Hairy cell leukemia Clonal B cells
MDS with Fibrosis = descriptive term that includes primary MDS (often RAEB2) with fibrosis and therapy related myeloid neoplasms with fibrosis

Secondary Marrow Fibrosis

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