BACKGROUND Somatic mutations in the Janus kinase 2 gene (JAK2) occur in many myeloproliferative neoplasms, but the molecular pathogenesis of myeloproliferative neoplasms with nonmutated JAK2 is obscure, and the diagnosis of these neoplasms remains a challenge. METHODS We performed exome sequencing of samples obtained from 151 patients with myeloproliferative neoplasms. The mutation status of the gene encoding calreticulin (CALR) was assessed in an additional 1345 hematologic cancers, 1517 other cancers, and 550 controls. We established phylogenetic trees using hematopoietic colonies. We assessed calreticulin subcellular localization using immunofluorescence and flow cytometry. RESULTS Exome sequencing identified 1498 mutations in 151 patients, with medians of 6.5, 6.5, and 13.0 mutations per patient in samples of polycythemia vera, essential thrombocythemia, and myelofibrosis, respectively. Somatic CALR mutations were found in 70 to 84% of samples of myeloproliferative neoplasms with nonmutated JAK2, in 8% of myelodysplasia samples, in occasional samples of other myeloid cancers, and in none of the other cancers. A total of 148 CALR mutations were identified with 19 distinct variants. Mutations were located in exon 9 and generated a +1 base-pair frameshift, which would result in a mutant protein with a novel C-terminal. Mutant calreticulin was observed in the endoplasmic reticulum without increased cell-surface or Golgi accumulation. Patients with myeloproliferative neoplasms carrying CALR mutations presented with higher platelet counts and lower hemoglobin levels than patients with mutated JAK2. Mutation of CALR was detected in hematopoietic stem and progenitor cells. Clonal analyses showed CALR mutations in the earliest phylogenetic node, a finding consistent with its role as an initiating mutation in some patients. CONCLUSIONS Somatic mutations in the endoplasmic reticulum chaperone CALR were found in a majority of patients with myeloproliferative neoplasms with nonmutated JAK2. (Funded by the Kay Kendall Leukaemia Fund and others.)

Methotrexate (MTX) has become the first-line treatment for rheumatoid (RA) and psoriatic arthritis (PsA); however, few studies have focused on its tolerability. The objective of our analyses was to study RA and PsA patients in whom MTX was discontinued, the reasons for this and the duration of MTX treatment prior to withdrawal. A retrospective electronic database review was undertaken to identify all patients who had received MTX for RA or PsA. Patients who had discontinued MTX were then identified, and the reasons for this were categorised. The duration of MTX treatment was assessed in those who had stopped treatment due to intolerability. A total of 1,257 patients who had received MTX were identified [762 (61 %) RA and 193 (15 %) PsA]. MTX had been stopped in 260 (34 %) patients with RA and 71 (36 %) patients with PsA most commonly due to gastrointestinal intolerability. The median duration of MTX treatment was 10 months in both groups, mean duration 21 and 18.6 months in RA and PsA groups, respectively. Overall, one third of patients with RA and PsA stop MTX most commonly due to poor tolerability. In the context of chronic disease, the median duration of treatment is short (10 months). Our analysis did not include patients who suffer from side effects but continue therapy; thus, the magnitude of the problem may be substantially greater therefore as poor tolerability impacts treatment adherence.

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