A Novel Pathogenic CALR Exon 9 Mutation in a Patient with Essential Thrombocythemia

: The clinical phenotypes and prognoses of CALR-mutant myeloproliferative neoplasms depend on the mutation type. The 2 most common mutations, type 1 (52-bp deletion) and type 2 (5-bp insertion), account for 85% of CALR-mutated neoplasms. The former confers a myelofibrotic phenotype, and the latter is associated with a low risk of thrombosis and an indolent clinical course. Individual case reports for patients with novel pathogenic CALR mutations are rare. Herein, we present the first case in the literature, to our knowledge, of a 63-year old ethnic Korean man with essential thrombocythemia who was diagnosed with a novel +1-bp frameshift mutation in CALR, which was predicted to exhibit a type 2-like phenotype.