Calreticulin molecular testing aids diagnosis and classification of MPNs by revealing mutations in the majority of JAK2 and MPL mutation-negative patients.
Somatic mutations in the calreticulin gene CALR are detected in peripheral blood in the ~65-85% of essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients that are JAK2- and MPL-mutation negative.1,2 Molecular analysis of these three genes now allows these disease markers to be identified in >90% of MPN patients1-3, helping to classify the disease and differentiate it from a reactive process. CALR mutation testing also has prognostic value as CALR mutations are associated with longer survival and fewer thrombotic events compared to JAK2 mutations.1-4
Calreticulin is a calcium-binding protein involved in signaling and protein expression that is believed to be responsible for clearing misfolded proteins and involved in expression regulation. CALR mutations reported in myeloproliferative neoplasms create translation frameshifts in exon 9 which truncate the C-terminal calcium binding domain and create a novel C-terminal peptide.1,2 Initial reports support CALR mutations as early and disease-initiating mutations1,2,4 that favor expansion of the megakaryocytic lineage.4 CALR mutations are mutually exclusive with JAK2 or MPL mutations.1-3
NeoGenomics clients can obtain complete molecular characterization of their MPN cases by:
- Ordering CALR mutation analysis on previously-tested patients
- Analyzing CALR within the MPN Extended Reflex Panel which includes sequential testing of JAK2 V617F, JAK2 Exon 12-14, CALR, and MPL
CALR in Essential Thrombocythemia (ET)
CALR mutations occur in approximately 25% of ET overall2 and 49-67% of JAK2- and MPL- negative ET.2, 4 Patients with CALR-mutated ET tend to be younger3 and have higher platelet counts and lower hemoglobin than those with JAK2-mutated ET.2-4
Risk of thrombosis is lower in CALR-mutated ET patients than those with JAK22-4 or MPL mutations4 and compares with the risk of mutation-negative patients.4
Evidence for long-term prognosis of CALR-mutated ET is unfolding. Longer overall survival for these patients, compared to JAK2-positive ET, has been reported2 but not observed in all studies.1, 3, 4 Increased thrombosis-free survival in CALR-positive cases has been reported.4
An increased incidence of transformation to myelofibrosis was seen in one study2 but not observed in others.3, 4
CALR in Primary Myelofibrosis (PMF)
CALR mutations were detected in 88% PMF patients without JAK2 and MPL mutations.2 PMF patients with CALR mutations are reported to have longer overall survival than those with JAK2 and MPL mutations.2
CALR in Polycythemia Vera (PV) and other hematologic disorders
CALR mutations are not reported in PV patients. In two studies with 430 total PV patients, no mutations were found.1, 2 Testing can therefore be used to distinguish PV patients from those with ET or PMF. Mutations are reported in 8% of patients with MDS, rarely found in CMML or atypical CML, and not reported in lymphoid leukemia or solid tumors.1
CALR Mutation Analysis Test Detail
Description:Testing is performed by bi-directional sequencing of exon 9 of the CALR (calreticulin) gene and fragment length analysis for enhanced detection and quantitative reporting of insertion/deletion mutations (indels). Results positive for insertions/deletions are reported as a percentage mutant peak relative to wild-type peak. This percentage may be used for monitoring. Testing is performed on plasma for increased sensitivity whenever possible.
- Peripheral blood: 5 mL in EDTA tube
- Bone marrow: 2 mL in EDTA tube
Storage and Transportation:
Use cold pack for transport, making sure cold pack is not in direct contact with specimen. Ship same day as drawn whenever possible; specimens
- Nangalia J, Massie CE, Baxter EJ, et al. Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2. N Engl J Med. 2013;369(25):2391-405.
- Klampfl T, Gisslinger H, Harutyunyan AS, et al. Somatic mutations of calreticulin in myeloproliferative neoplasms. N Engl J Med. 2013;369(25):2379-90.
- Rumi E, Pietra D, Ferretti V, et al. JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes. Blood. 2014;123(10):1544-51.
- Rotunno G, Mannarelli C, Guglielmelli P, et al. Impact of calreticulin mutations on clinical and hematological phenotype and outcome in essential thrombocythemia. Blood. 2014;123(10):1552-5.