Marrow remodeling is associated with adverse co-mutational complexity in CALR-mutated primary myelofibrosis: a clinicopathologic study

Calreticulin ( CALR ) mutations are present in 20–30% of patients with primary myelofibrosis (PMF), but the relationship between marrow remodeling and molecular alterations across disease stages in CALR -mutated PMF patients remains incompletely understood. In this cross-sectional study, we analyzed 70 CALR -mutated PMF cases (42 prefibrotic/early PMF and 28 overt fibrotic PMF; 46 cases with CALR type 1 mutations and 24 cases with CALR type 2 mutations) using a 38-gene targeted next-generation sequencing panel and quantitative review of diagnostic trephine biopsies. The variant allele frequency (VAF) of CALR mutation did not differ significantly between pre-PMF and overt PMF within either subtype. In contrast, overt PMF was associated with a higher prevalence of additional mutations (18/28 vs 8/42; P < 0.001) and prespecified adverse non-driver mutations (13/28 vs 3/42; P < 0.001). ASXL1 and EZH2 mutations were also more prevalent in overt PMF. Histologically, overt PMF was characterized by higher reticulin grade, fewer megakaryocytes and tight clusters, fewer large megakaryocytes, and more dysplastic forms and naked nuclei. These findings suggest that marrow remodeling is associated with adverse co-mutational complexity and may provide a tissue-level correlate of stage-related molecular alterations in patients with CALR -mutated PMF. Longitudinal studies and comparative cohorts with other driver mutations are required to validate these findings and determine their broader applicability.