Impact of Minimal Residual Disease after Allografting Detected By JAK2V617F, MPL or Calreticulin in Myelofibrosis Patients

Introduction:

Residual minimal disease (MRD) in hematological malignancies has become a valid tool to predict clinical relapse after allogeneic stem cell transplantation (ASCT).

Methods and Patients:

We screened 154 patients with myelofibrosis who underwent ASCT for molecular residual disease by qPCR or next-generation sequencing (NGS) for JAK2V617F, MPLW515L and MPLW515K or Calreticulin (L367fs*46, and K385fs*47) mutations in peripheral blood (PB) on days +100 and +180 after transplantation. Out of 154 pts, 103 were JAK2V617F (n=101), 31 Calreticulin (CALR), and 4 MPL mutated, while 13 pts were triple negative. 136 pts could be followed after ASCT with one molecular marker. The median age of the pts was 58 years (range, 32-75 y). Patients had either primary myelofibrosis (n= 90), post ET/PV myelofibrosis (n=40), myelofibrosis in acceleration or were transformed to AML (n=6). Conditioning mainly relied on a busulfan-based reduced-intensity regimen. Donor were HLA-identical sibling (n=26), matched unrelated (n=71) or mismatched unrelated (n=39). JAK2V617F, MPL, and CALR mutations were measured by usage of Taqman PCR or in case of CALR Type 2 mutation by digital PCR on day +100 and day +180 from PB as described elsewhere.

Results:

After a median follow up of 78 months (range, 49-101 months) the 5-year estimated overall survival was 60% (95% CI: 50-70%) and the cumulative incidence of relapse at 5 years was 26% (95% CI: 18-34%) for the entire study population. On days +100 and +180 after transplantation in 27% and 12% of the patients the underlying mutation was still detectable in peripheral blood. The percentage of complete clearance was higher in CALR-mutated patients (96%) in comparison to MPL (75%) and JAKV2617F (70%) mutated pts. Whereas there was a trend for better survival for CALR-mutated patients in comparison to JAK2-mutated patients (71% vs 57%; p=0.48), once a patient achieved molecular remission post-transplant the risk of relapse remained low independently of the underlying mutation. Patients who were alive and without relapse at days +100 or +180 but with  still detectable mutation in PB had a significantly higher risk of relapse than those who were molecular negative (62% vs 10%, p<0.001; and 70% vs 10%, p<0.001, respectively). In a multivariate analysis only high-risk disease status (HR 2.5; 95% CI: 1.18-5.25, p=0.016) and detectable MRD at day 180 (HR 8.36, 95% CI: 2.76-25.30, p<0.001) were significant factors for a higher risk of relapse.

Conclusions:

JAK2V617F, CALR and MPL genetic lesions allow to monitor MRD in around 90% of the myelofibrosis patients after ASCT by qPCR or digital PCR in the PB. Persistence of MRD on days +100 or +180 in peripheral blood can be used to taper immunosuppressive drugs or to apply donor lymphocyte infusion to prevent clinical relapse.