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.