Guidelines for myelofibrosis were produced in 2012 (Reilly et al, 2012), but since then Ruxolitinib, a JAK1/JAK2 inhibitor, has been approved for use in the European Union and highly prevalent mutations in the Calreticulin gene (CALR) have been described.

We therefore wish to revise the existing guideline (Reilly et al, 2012) to accommodate this important data. Current diagnostic criteria should be modified to incorporate testing for the CALR mutations into major criteria A2 alongsideJAK2 V617F, as shown in Table 1 (Evidence grade 1A). Patients with CALR mutations may have a better prognosis (Klampfl et al, 2013), but this has not formally been assessed and incorporated into prognostic scores.

Declaration of Interests

The BSH paid the expenses incurred during the writing of this guidance. None of the authors had conflicts of interest to declare. All authors have made a declaration of interests to the BSH and Task Force Chairs which may be viewed on request.