CHAPTER 16: Myeloproliferative Neoplasms

MPNs include myelofibrosis (MF), polycythemia vera (PV), and essential thrombocythemia (ET). They are characterized by being Philadelphia chromosome–negative.

A 56-year-old woman is admitted to the emergency room with a severe case of pharyngitis. In addition to her symptom of pharyngitis, a peripheral blood count reveals 1 × 10⁶ platelets/dL. She is told she has ET. Blood is drawn for determination of JAK2 mutations.

• Schedule bone marrow aspiration and biopsy

• Obtain blood for determination of JAK2 mutations

• Start patient on acetylsalicylic acid (low-dose aspirin)

MPNs are a group of heterogeneous disorders that are characterized by a risk of transformation to acute myeloid leukemia and are collectively Philadelphia chromosome–negative. The profile varies for each type, but indications often include constitutional symptoms, fatigue, pruritus, weight loss, splenomegaly, and laboratory abnormalities such as erythrocytosis, thrombocytosis, and leukocytosis. Patients with MF have worse survival than patients with PV and ET. MPNs are diagnosed by identifying driver mutations such as JAK2, CALR, and MPL mutations.¹

• MPNs are not associated with chromosomal abnormalities

1. Mesa R, Miller CB, Thyne M, et al. Myeloproliferative neoplasms (MPNs) have a significant impact on patients’ overall health and productivity: the MPN Landmark survey. BMC Cancer 2016;16:167.

The mutations associated with MPNs are: JAK2 mutations, the thrombopoietin receptor (MPL), and the calreticulin gene (CALR).¹

JAK2 V617F (exon 14) accounts for >90% of patients with PV and 60% of patients with ET or MF. Exon 12 JAK2 mutations account for 2%–3% of patients with PV. MPL mutations are reported in 5%–8% of MF patients and 1%–4% of ET patients.

The CALR gene has two types of mutations in the exon 9: type 1 and type 2. Type 1 is frequent in MF patients and type 2 in ET patients. CALR gene mutations account for 60%–80% of ALL JAK2/MPL-negative ET and MF patients. Other mutations such as EZH2 and TP53 have also been reported in MPN patients.²

• Patients with CARL mutations have better prognosis than those with JAK2/MPL mutations, and those with CARL mutations type 1 have better survival than those with type 2

• Patients with CARL mutations have better prognosis than those with triple-negative MPNs

• CALR type 1 mutations are 52 base pair deletions, and CALR type 2 are 5 base pair insertions

1. Kralovics R, Passamonti F, Buser AS, et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med 2005;352(17):1779-90.

2. Beer PA, Campbell PJ, Scott LM, et al. MPL mutations in myeloproliferative disorders: analysis of the PT-1 cohort. Blood 2008;112(1):141-9.