(38)CHU Angers, Laboratoire d'hématologie, ANGERS, France
Among Philadelphia chromosome negative myeloproliferative neoplasms (MPN), myelofibrosis is
associated with the worst prognosis and its evolution is extremely variable according to
prognostic features and treatment.
In this study, we aimed to characterize the molecular landscape of 479 patients with primary
or secondary myelofibrosis recruited from 24 French Intergroup of Myeloproliferative
Neoplasms (FIM) centers. A custom Next-Generation Sequencing (NGS) panel covering all
exons of 77 genes was performed and only exonic or splicing mutations (donor and acceptor
sites) with a variant allele frequency (VAF) above 2% and not described as common
polymorphisms were retained. Variants were classified according to their putative pathogenic
effect as pathogenic, likely pathogenic, or variant of unknown significance. A Bayesian
network allowed the identification of genomic groups whose prognostic impact was then
studied using a multistate model considering transitions from the 3 conditions: myelofibrosis,
acute leukemia, and death. Variant of unknown significance were not retained in the statistical
analysis. Results were validated using an independent, previously published cohort (n=276).
A total of 1385 additional variants were detected with the following distribution: 861
pathogenic variants, 179 likely pathogenic variants, and 345 variants of unknown significance.
We found a median of 3 additional variants per patient (range: 0-11), and a median of 2 0-
10 additional mutations when considering only pathogenic and likely pathogenic variants.
The most frequently mutated genes were ASXL1, TET2, SRSF2, U2AF1 and EZH2. Using a
Bayesian network, four genomic groups were identified: (i) patients with TP53-mutation, (ii)
patients with at least one mutation in EZH2, CBL, U2AF1, SRSF2, IDH1, IDH2,
NRAS, or KRAS (high-risk group), (iii) patients with ASXL1-only mutation (i.e. no associated
mutation in TP53 or high-risk genes), and (iv) other patients. Multistate model found that
both TP53 and high-risk groups were associated with leukemic transformation (HR: 8.68 3.32-
22.73 and 3.24 1.58-6.64 respectively) and death from myelofibrosis (HR: 3.03 1.66-5.56
and 1.77 1.18-2.67 respectively). ASXL1-only mutations had no prognostic value that was
confirmed in the validation cohort. However, ASXL1 mutations conferred a worse prognosis
when associated with a mutation in TP53 or high-risk genes.
This study provides a new definition of adverse mutations in myelofibrosis with the addition
of TP53, CBL, NRAS, KRAS and U2AF1 to previously described genes. Furthermore, our results
argue that ASXL1 mutations alone cannot be considered detrimental.