The prognostic advantage of calreticulin mutations in myelofibrosis might be confined to type 1 or type 1-like CALR variants.

To the editor: Approximately 90% of patients with primary myelofibrosis (PMF) harbor JAK2 (58%), CALR (25%), or MPL (7%) mutations.[1][1][⇓][2]-[3][3] CALR -mutated PMF patients are younger than their JAK2 -mutated counterparts, and they display higher platelet count, lower leukocyte count,