Myelofibrosis (MF)

Myelofibrosis (MF) is a bone marrow disorder in which the marrow is replaced with fibrous scar tissue.¹ MF may be primary, arising in the absence of preceding myeloproliferative pathology, or secondary, developing from another bone marrow disorder, such as polycythemia vera (PV) or essential thrombocythemia (ET).² 

The main pathogenic mechanism of primary myelofibrosis (PMF), which is a myeloproliferative neoplasm (MPN), is deregulation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathways. A driver mutation in the JAK2, MPL (myeloproliferative leukemia), or CALR (calreticulin) gene is present in the majority of patients with PMF.³ 

Diagnosis of PMF is based on current World Health Organization (WHO) criteria involving both clinical and laboratory features. Diagnosis of secondary MF, often post-polycythemia vera (post-PV) MF and post-essential thrombocythemia (post-ET) MF, should follow criteria published by the International Working Group for MPN Research and Treatment (IWG-MRT).⁴ Various tests are essential to determine if a patient meets the criteria for MF.

Laboratory testing for MF

Complete Blood Cell Count

The results of blood cell counts are not conclusive in the diagnosis of MF because the counts change from time to time in affected persons.⁵ In the initial, prefibrotic stages of MF, the cell counts are either normal or increased. A mild increase in neutrophils with a left shift may be present. The platelet count may be mildly to moderately increased. However, in the overt or fibrotic stage, the platelets are abnormally large with a bizarre appearance and reduced in number (thrombocytopenia). Leukoerythroblastosis and anemia may also be seen,⁶ as well as abnormal, teardrop-shaped red blood cells and immature blasts.⁷ 

Following the WHO diagnostic criteria, a complete blood count (CBC) can scan for the PMF minor criteria of unexplained anemia and leukocytosis ≥ 11 × 10⁹/L. If diagnosing secondary MF, the CBC can also scan for its minor criteria of anemia, loss of phlebotomy, and  ≥ 2 g/dL decrease in hemoglobin level.⁴ 

Read more about MF guidelines

Blood Chemistry Profile

This testing calculates the amounts of various substances released into the blood by tissues and organs, such as electrolytes (eg, sodium, potassium, and chloride), lipids, proteins, glucose, uric acid, and enzymes. The results show how effectively the liver, kidneys, and other organs are functioning. Serum levels of lactic dehydrogenase (LDH), uric acid, bilirubin, and alkaline phosphatase are frequently high in patients with MF. Patients with elevated serum LDH meet a minor criteria for PMF. Additionally, the total iron-binding capacity and serum levels of iron, ferritin, and erythropoietin may be assessed.⁷ 

Read more about MF diagnosis

Bone Marrow Aspiration and Biopsy Testing for MF

Bone marrow testing consists of 2 steps: aspiration and biopsy. This examination is necessary to differentiate MF from other MPNs.⁷ Bone marrow aspiration and biopsy can confirm the diagnosis of MF by providing evidence of grade 2 or higher bone marrow fibrosis.⁸

Prefibrotic PMF Indications 

Bone marrow in prefibrotic PMF is hypercellular, with large, dysplastic, clustered megakaryocytes and increased granulocytes. The megakaryocytes are characterized by an aberrant nuclear/cytoplasmic ratio and hyperchromatic, bulbous, or irregularly folded nuclei. The megakaryocyte features are useful for distinguishing prefibrotic PMF from ET. Reticulin stain reveals increased reticulin surrounding clusters of megakaryocytes.⁶ 

Overtly Fibrotic PMF Indications 

Bone marrow in overtly fibrotic PMF is hypocellular, with diffuse fibrosis and atypical streaming of megakaryocytes. The bone marrow tap is dry and characterized by osteosclerosis with broad and irregular bony trabeculae and significantly dilated sinuses.⁶

Read more about MF clinical features

Molecular Testing for MF

Molecular testing identifies unusual alterations in the patient’s cancer cell genes, chromosomes, proteins, or other components. If bone marrow fibrosis has been discovered, it’s important to follow with genetic testing, as it often confirms JAK2, CALR, or MPL gene mutations — another major criteria required for a diagnosis of MF.⁴

Cytogenetic Analysis (Karyotyping)

Bone marrow cytogenetic investigations are useful to rule out chronic myelogenous leukemia, myelodysplastic syndrome, and other chronic myeloid diseases. However, because the bone marrow tap is dry in more than 50% of patients with PMF, it can be difficult to obtain material for cytogenetic studies.⁹ Karyotype abnormalities are found in up to 50% of cases of PMF. Frequent karyotype abnormalities include del(20q), del(13q), +8, +9, and 1q. The presence of der(6)t(1;6)(q21-23;p21.3) or del(13)(q12-22) is strongly suggestive of primary MF.⁶

Read more about MF comorbidities

Polymerase Chain Reaction Testing

Small quantities of specific DNA fragments are amplified in polymerase chain reaction (PCR) testing so that they can be easily identified and analyzed in a cell sample. PCR can be used to determine whether specific genetic mutations are present. Both blood and bone marrow samples can be used for PCR analysis. The JAK2, MPL, or CALR gene is mutated in almost 90% of patients with MF.⁷

DNA Sequencing

DNA sequencing may be performed in both blood and bone marrow samples. By comparing the DNA sequence of cancer cells with that of normal cells, genetic alterations can be identified that are specific to cancer cells and cause them to grow.⁷ 

An approximation of the frequencies of common mutations found in patients with MF includes:

• JAK2  V617F mutation, 60%; 
• CALR mutation, 20% to 35%; 
• MPL mutation, 5% to 8%; and 
• “Triple-negative MF”: triple negativity for mutations in JAK2, CALR, and MPL (8% to 12%).^6,7 

Other genetic variants may be relevant, and mutations in several other genes have been discovered in individuals with PMF, including CBL, LNK/SH2B3, ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2, DNM3TA, SF3B1, SRSF2, and U2AF1. These mutations have been found in individuals with JAK2, CALR, or MPL mutations. Researchers are investigating the role of these mutations along with other mutations in the onset and progression of MF.⁷ 

Overall survival correlates with the driver mutational profile. Survival rates are higher in patients with CALR mutations than in those with other mutations. Survival rates are lowest among patients with triple-negative MF.⁶ 

Read more about MF genetics

​​HLA Typing

Patients with MF who are potential candidates for allogeneic stem cell transplant should undergo human leukocyte antigen (HLA) typing. HLAs help the body differentiate between its own cells and foreign cells and have a significant role in the immunological response to foreign substances. Before a patient is approved for stem cell transplant, HLA matching is done to improve surgical outcome with positive matching of donor and recipient. This vastly improves engraftment and reduces postsurgical complications.⁷

Read more about MF surgical management

References

1. Myelofibrosis. MedlinePlus. Accessed December 10, 2022. 
2. Silver RT. What is primary myelofibrosis vs. secondary myelofibrosis? Weill Cornell Medicine. Accessed December 10, 2022.
3. Takenaka K, Shimoda K, Akashi K. Recent advances in the diagnosis and management of primary myelofibrosis. Korean J Intern Med. 2018;33(4):679-690. doi:10.3904/kjim.2018.033 
4. Tefferi A. Primary myelofibrosis: 2021 update on diagnosis, risk-stratification and management. Am J Hematol. 2021;96(1):145-162. doi:10.1002/ajh.26050
5. Primary myelofibrosis. NORD (National Organization for Rare Disorders). Accessed December 10, 2022. 
6. Kaseb H, Hudnall SD. Primary myelofibrosis. PathologyOutlines.com. Updated September 29, 2022. Accessed December 10, 2022.
7. Myelofibrosis diagnosis. Leukaemia and Lymphoma Society. Accessed December 10, 2022. 
8. Myelofibrosis diagnosis. Mayo Clinic. Accessed December 10, 2022. 
9. Lal A. Primary myelofibrosis workup. Medscape. Updated September 21, 2022. Accessed December 10, 2022.

Reviewed by Debjyoti Talukdar, MD, on 12/27/2022.

---

Harshi Dhingra, MD

Harshi Dhingra is a licensed medical doctor with specialization in Pathology. She is currently employed as faculty in a medical school with a tertiary care hospital and research center in India. Dr. Dhingra has over a decade of experience in diagnostic, clinical, research, and teaching work, and has written several publications and citations in indexed peer reviewed journals. She holds medical degrees for MBBS and an MD in Pathology.