CALR Mutated Essential Thrombocythemia is a distinct disease

JAK2 or CALR mutation status defines subtypes of ET with substantially different clinical course and outcomes

Key Points

  • JAK2 (V617F) mutated essential thrombocythemia and polycythemia vera are different phenotypes in the evolution of a single neoplasm

  • CALR mutated essential thrombocythemia is a distinct disease entity not only at molecular level but also with respect to clinical outcomes


Patients with essential thrombocythemia may carry JAK2 (V617F), an MPLsubstitution, or a CALR mutation. We studied biologic and clinical features of essential thrombocythemia according to JAK2 or CALR mutation status, and in relation to those of polycythemia vera. The mutant allele burden was lower inJAK2 mutated than in CALR mutated essential thrombocythemia. Patients withJAK2 (V617F) were older, and had higher hemoglobin level and white blood cell count, and lower platelet count and serum erythropoietin than those with CALRmutation. Hematologic parameters of patients with JAK2 mutated essential thrombocythemia or polycythemia vera were related to the mutant allele burden.

While no polycythemic transformation was observed in CALR mutated patients, the cumulative risk was 29% at 15 years in those with JAK2 mutated essential thrombocythemia. There was no significant difference in myelofibrotic transformation between the 2 subtypes of essential thrombocythemia. Patients with JAK2 mutated essential thrombocythemia and those with polycythemia vera had a similar risk of thrombosis, which was twice that of patients with CALR mutation.

These observations are consistent with the notion that JAK2 mutated essential thrombocythemia and polycythemia vera represent different phenotypes of a single myeloproliferative neoplasm, while CALR mutated essential thrombocythemia is a distinct disease entity.

For more information on this important discovery, check out the recent article on MPNforum – CALR: JAK for the Rest of Us

Link to Original Article
About David Wallace

Founder of PV Reporter, a resource for Myeloproliferative Neoplasm (MPN) patients and caregivers. After being diagnosed with Polycythemia Vera (PV) in 2009, I utilized social media to connect with "informed patients" and develop a better understanding of emerging treatment options. My philosophy on patient care is straight forward - "educating the patient is essential, so the patient can guide their physician to meet his or her needs." PV Reporter is a comprehensive resource hub giving visitors vital tools to become "empowered patients."

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