JAK2 V617F Mutational Status in Myelofibrosis at and before Disease Progression Including Leukemic Transformation: A Longitudinal Study in 68 Patients.

Background: An acquired point mutations of JAK2 (V617F) was recently described in a substantial proportion of patients with myeloproliferative disorders (MPD), including myelofibrosis with myeloid metaplasia (MMM). The current study examines i) JAK2 V617F mutational status at time of leukemic transformation (LT) of MMM and its clinical correlates, ii) the possibility of changes over time in mutational status in MMM patients that have either undergone leukemic transformation (LT) or experienced disease progression.

Methods: Mutation analysis for JAK2 V617F was performed in DNA derived from either peripheral blood mononuclear cells (PBMC) (i.e. fresh specimens) using genomic DNA amplified by PCR, or extracted from cytogenetic pellets in archived specimens. Fluorescent dye chemistry sequencing was performed using the same primers used for amplification.

Results: The study population consisted of 68 patients including 33 patients with disease transformation into AML.

i. MMM patient cohort with LT (n=33). The JAK2 V617F mutant allele was detected in 21 of the 33 patients (64%; homozygous in 6%) at the time of LT. As expected, PPMM was over-represented in the group with the mutation but the presence of the mutation affected neither the clinical presentation at time of LT or overall outcome. Furthermore, in 9 patients (7 heterozygotes and 2 with wild-type allele), archived bone marrow that was collected at a median of 23 months (range, 3–105) before LT was available and disclosed no change in mutational status.

ii. MMM patient cohort with disease progression without LT (n=35; 19 AMM, 9 PPMM, 7 PTMM): Each patient in this group had at least two bone marrow or peripheral blood samples that were collected at two different time points separated by a median of 18.2 months (range (3–82). Of the total 35 patients in this group, 32 (91%) showed no change in JAK2 V617F mutational status over time including 3 patients in whom the first sample was collected before they transformed into MMM from antecedent PV or ET. In the remaining 3 patients, a switch from wild-type to heterozygous state (1 patient), and heterozygous to homozygous (2 patients), was documented after 78, 43, and 83 months, respectively.

Conclusions: In most instances, JAK2 V617F mutational status in MMM remains unchanged over time including during leukemic transformation. Furthermore, the presence of the mutation in MMM-related LT does not appear to affect clinical outcome. These observations undermine the role of JAK2 V617F in either disease progression or LT in MMM.