CALR type 1 mutations are associated with an increased incidence of myelofibrosis in young male patients

Background Calreticulin (CALR) mutations are commonly identified in patients with essential thrombocythaemia or myelofibrosis. CALR type 1 mutations are known to have a higher overall incidence in males but little is known about the risks of mutation subtypes on myelofibrotic change across patient age and sex. Aims To identify differences in the incidence of myelofibrotic change within subgroups of patients with CALR type 1 mutations. Methods All patients with a positive CALR exon 9 mutation identified within our unit between February 2016 and September 2020 were reviewed with note taken of patient sex, age at diagnosis, initial MPN diagnosis, and subsequent disease transformation. Results In our cohort, young male patients with CALR type 1 mutations were shown to be at significantly increased risk of myelofibrosis compared to age matched female patients. Conclusions Male patients have a worse myeloproliferative neoplasm phenotype than female patients with it occurring at a younger age and being more myelofibrotic in nature. Further investigation is needed into the reasons for this variability.