Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations

Abstract

Somatic insertions/deletions in the calreticulin gene have recently been discovered to be causative alterations in myeloproliferative neoplasms. A combination of qualitative and quantitative allele-specific polymerase chain reaction, fragment-sizing, high resolution melting and Sanger-sequencing was applied for the detection of three driver mutations (in Janus kinase 2, calreticulin and myeloproliferative leukemia virus oncogene genes) in 289 cases of essential thrombocythemia and 99 cases of primary myelofibrosis. In essential thrombocythemia, 154 (53%) Janus kinase 2 V617F, 96 (33%) calreticulin, 9 (3%) myeloproliferative leukemia virus oncogene gene mutation-positive and 30 triple-negative (11%) cases were identified, while in primary myelofibrosis 56 (57%) Janus kinase 2 V617F, 25 (25%) calreticulin, 7 (7%) myeloproliferative leukemia virus oncogene gene mutation-positive and 11 (11%) triple-negative cases were identified. Patients positive for the calreticulin mutation were younger and had higher platelet counts compared to Janus kinase 2 mutation-positive counterparts. Calreticulin mutation-positive patients with essential thrombocythemia showed a lower risk of developing venous thrombosis, but no difference in overall survival. Calreticulin mutation-positive patients with primary myelofibrosis had a better overall survival compared to that of the Janus kinase 2 mutation-positive (P=0.04) or triple-negative cases (P=0.01). Type 2 calreticulin mutation occurred more frequently in essential thrombocythemia than in primary myelofibrosis (P=0.049). In essential thrombocythemia, the calreticulin mutational load was higher than the Janus kinase 2 mutational load (P<0.001), and increased gradually in advanced stages. Calreticulin mutational load influenced blood counts even at the time point of diagnosis in essential thrombocythemia. We confirm that calreticulin mutation is associated with distinct clinical characteristics and explored relationships between mutation type, load and clinical outcome.

Copyright© Ferrata Storti Foundation.

Figures

Figure 1.

Kaplan-Meier analysis of overall survival in patients with ET (panel A, n=261) and PMF (panel B, n=87) according to the presence of different driver mutations. Patients qualified for triple-negative status if JAK2mut and CALRmut and MPLmut were all absent. For a subset of patients (ET: n=2, PMF: n=11) treated by hematopoietic stem cell transplantation, the follow-up was censored at the date of this intervention. In ET, univariate analyses resulted in an overall P value of 0.846 (A). In PMF, the same comparison gave a P value of 0.023 (B). Upon pairwise univariate comparisons, the CALRmut subgroup showed significantly better survival compared to JAK2mut (P=0.04) and triple-negative (P=0.01) PMF patients while JAK2mut patients showed only a tendency towards better overall survival compared to triple-negative patients (P=0.076). ET: essential thrombocythemia; PMF: primary myelofibrosis.

Figure 2.

Comparisons of relative quantities of driver mutations (JAK2 V617F or CALR) in different MPN subgroups according to diagnosis and the relation of time of sampling and time of diagnosis. The first row under the x axis shows the number of patients (n) in the respective subgroups. If no primary or secondary myelofibrosis was present at the time of sampling, sampling within 1 year of diagnosis qualified, as seen in the second lines, as “<1 year”; all other situations were allocated into the “>1 year” subgroup. If primary or secondary myelofibrosis was present at the time of sampling, no such subgrouping was performed (“secondary or primary MF”). Quantification of the respective driver mutation was performed by real-time quantitative allele-specific PCR (JAK2 V617F) or fragment analysis (CALR exon 9). Pairwise comparisons were performed with the Mann-Whitney test. ET: essential thrombocythemia; PMF: primary myelofibrosis; MF: myelofibrosis; PV: polycythemia vera.