BACKGROUND: Activation of the JAK/STAT signaling pathway is a hallmark feature of myelofibrosis (MF), and is driven by mutations in JAK2, CALR, and MPL. However, up to 10% of patients with MF lack mutations in these driver genes, termed “triple-negative MF.” Triple-negative MF portends a poor prognosis, with higher rates of leukemic transformation and shorter survival.
OBJECTIVE: We aimed to further characterize the clinical and genomic features of patients with triple-negative MF.
METHODS: We performed next generation sequencing (NGS) on peripheral blood or bone marrow samples from patients with myelofibrosis at the University of Michigan using a CLIA-certified Laboratory Developed Test (LDT) designed to efficiently identify non-synonymous somatic point mutations in a panel of 1700+ genes with suggestive links to cancer. The assay includes 24,774 deeply sequenced capture targets that together cover all or part of 1,711 genes and spans approximately 3.8Mb of the human exome. Somatic insertions and deletions and copy number aberrations, as well as gene fusions and outlier gene expression, are reported.
RESULTS: We identified 7 cases of triple-negative MF. Clinical features were heterogeneous. DIPSS-plus scores range from 1-5. To date, no patient has experienced a leukemic transformation, and 6 remain alive. Three patients had concurrent autoimmune conditions, and two had pulmonary hypertension. Cytogenetic and molecular features were also heterogeneous. Normal karyotype was seen in 3, a high-risk karyotype (i17q) in 1, del(13q) in 2, and unknown in 1. By NGS, the median number of genes mutated was 3 (range 0-14). Two patients had no abnormalities found; both also had normal karyotypes and one had a history of autoimmunity. Other mutated genes included those involved in DNA damage repair (TP53 in 2, ATM in 1, and RAD51 in 1), epigenetic modifiers (ASXL1 in 3, DNMT3A in 1), and splicing factors (SRSF2 in 2, U2AF1 in 1).
CONCLUSION: Triple-negative MF represents a small subset of MF with heterogeneous clinical and genomic features, and includes a smaller cohort with no clonal markers in whom immune pathways may contribute. The pathophysiology and genomic drivers of triple-negative MF remain incompletely understood and warrant further study.
Funding for this research was provided by the D. Dan and Betty Kahn Foundation (PI Talpaz).