Outcomes of Allogeneic Hematopoietic Cell Transplantation in Patients With Myelofibrosis-A Systematic Review and Meta-Analysis

JAK Inhibitors for Myelofibrosis: Strengths and Limitations

PURPOSE OF REVIEW

The landscape of myelofibrosis (MF) has changed since the discovery of the JAK2 V617F mutation and subsequent development of JAK inhibitors (JAKis). However, treatment with JAKis remain a challenge. In this review we critically analyze the strengths and limitations of currently available JAK inhibitors.

RECENT FINDINGS

In MF patients, JAK inhibitors have been associated with reduced symptom burden and spleen size, as well as improved survival. However, durability of response and development of treatment resistance remain an issue. Recently, there has been increased efforts to optimize treatment with the development of highly selective JAK inhibitors, as well as use of combination agents to counter disease resistance through targeting aberrant signaling pathways. Treatment of MF patients with JAKi therapy can be challenging but the development of more potent and selective JAK inhibitors, as well as combination therapies, represent exciting treatment advances in this field.

When and how to transplant in myelofibrosis - recent trends

Allogeneic hematopoietic stem cell transplantation (AHSCT) is currently the only treatment modality that is capable of curing myelofibrosis (MF). Although outcomes of AHSCT have improved vastly in recent years owing to advancements in HLA typing, conditioning regimens, and supportive care, it remains a procedure with a considerable risk in MF patients due to conditioning regimen related toxicity, higher rates of graft failure, infections, and graft versus host disease (GVHD). Recent progress in the treatment and prevention of GVHD with post-transplant cyclophosphamide has also rendered transplantation from alternative donors feasible and safer, thus improving access to patients without HLA-identical donors. Accordingly, all patients with intermediate or high-risk MF today should be referred for potential transplant evaluation to consider the pros and cons of an early versus a delayed transplant strategy. Individual risk assessment in MF is best facilitated by contemporary prognostic models that incorporate both clinical and genetic risk factors. The current review highlights new information regarding risk stratification in MF, anchored by practical algorithms that facilitate patient selection for specific treatment actions, including AHSCT.

Transplant Outcomes in Myelofibrosis: Impact of Donor Type (Cord Blood Grafts Supported by CD34+ selected Cells [Haplo-Cord] Versus Matched Donors)

Despite the established potentially curative role of allogeneic hematopoietic cell transplantation (allo-HCT) in managing myelofibrosis (MF), the choice of alternative donors for patients lacking matched donors remains a challenge, and the optimal graft source in this disease entity continues to be an ongoing debate. We aimed to evaluate the impact of donor type: umbilical cord blood transplant supported with CD34+ selected haploidentical donor (haplo-cord) versus adult matched related donor (MRD) and matched unrelated donor (MUD) in 40 adult patients with primary or secondary MF, including those progressing to accelerated phase (AP) or blast phase (BP), who underwent their first allo-HCT. The primary objective of this study was to analyze the impact of stem cell source on primary endpoints of overall survival (OS), graft-versus-host disease, and non-relapse mortality (NRM). Median follow-up for all alive patients was 53 months (range 0.3-63 months). Nine patients (22.5%) underwent an MRD allo-HCT, 15 patients (37.5%) underwent a MUD allo-HCT, and 16 patients (40%) underwent a haplo-cord allo-HCT. Four patients died without neutrophil engraftment: 3 (19%) in haplo-cord group and one (4%) in MRD/MUD group. The cumulative incidence of absolute neutrophil engraftment by day 60 was 80% (95% CI 45-94) in the haplo-cord group and 92% (95% CI 65-98) in the MRD/MUD group (P = .09). The cumulative incidence of platelet engraftment by day 60 was 59% (95% CI 27-81) in haplo-cord group and 75% (95% CI 51-88) in MRD/MUD group (P = .4). OS was 62% at 1 year (95% CI 49-79) and 34% at 3 years (95% CI 21-55). The 3-year OS was similar between the haplo-cord group and the MRD/MUD (37% versus 32%, P = .9). The 1-year OS for AP/BP patients was 50% (95% CI 27-93) in the haplo-cord group, compared to 40% (95% CI 19-86) in the MRD/MUD. The 1-year OS for chronic phase CP patients was 83% (95% CI 58-100) in the haplo-cord group, compared to 79% (95% CI 60-100) in the MRD/MUD group. The cumulative incidence of relapse at 3 years in the haplo-cord group was 13% (95% CI 1.8-34), and in the MRD/MUD group was 28% (95% CI 10-49) (P = .36). One-year NRM was 38% (95% CI 15-61) in the haplo-cord group and 33% (95% CI 15-52) in the MRD/MUD group. Three-year NRM was 48% (95% CI 19-72) in the haplo-cord group and 54% (95% CI 29-73) in MRD/MUD group (P = .95). We showed no significant difference in OS, relapse, and NRM outcomes after haplo-cord transplant compared to adult matched donors' grafts (MRD or MUD) in MF patients. However, there were more graft failures in patients transplanted with a haplo-cord transplants and delayed engraftments with inadequate haplo myeloid bridges. Despite the small sample size in our study, considering our findings and the availability of other alternative donors, using haplo-cord platforms may no longer be justified for MF unless the UCB engraftment dynamics can be optimized.

Decision analysis for transplant candidates with primary myelofibrosis in the ruxolitinib era

The recent progress with ruxolitinib treatment might improve quality of life as well as overall survival in patients with primary myelofibrosis. Therefore, the optimal timing of allogeneic hematopoietic cell transplantation (HCT) in the ruxolitinib era remains to be elucidated. We constructed a Markov model to simulate the 5-year clinical course of transplant candidates with primary myelofibrosis and compared outcomes between those who underwent immediate HCT and those whose HCT was delayed until after ruxolitinib failure. Since older age was associated with an increased risk of mortality, we analyzed patients aged <60 and ≥60 years separately in subgroup analyses. Life expectancy was consistently longer in the groups undergoing delayed HCT after ruxolitinib failure regardless of the patients' age. Regarding quality-adjusted life years, a baseline analysis showed that immediate HCT was inferior to delayed HCT after ruxolitinib failure (2.19 vs. 2.26). In patients aged <60 years, immediate HCT was equivalent to delayed HCT after ruxolitinib failure (2.31 vs. 2.31). On the other hand, in patients aged ≥60 years, immediate HCT was inferior to delayed HCT after ruxolitinib failure (1.98 vs. 2.21). A one-way sensitivity analysis showed that the utility of being alive without chronic graft-versus-host disease after immediate HCT was the most influential parameter for quality-adjusted life years, and that a value higher than 0.836 could reverse the superiority of delayed HCT after ruxolitinib failure. As a result, delayed HCT after ruxolitinib failure is expected to be superior to immediate HCT, especially in patients aged ≥60 years, and is also a promising strategy even in those aged <60 years.

Improved Outcomes in Myelofibrosis after Allogeneic Stem-Cell Transplantation in the Era of Ruxolitinib Pretreatment and Intensified Conditioning Regimen-Single-Center Analysis

(1) Background: Allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is the only treatment with the potential for cure in patients with myelofibrosis (MF). However, the risk of graft rejection, which is particularly high in MF, and the risk of significant non-relapse mortality must be considered. (2) Methods: In this retrospective, single-center study, we compared allo-HSCT outcomes in 36 adult patients with MF transplanted at two-time intervals (2001-2015 versus 2016-2021). (3) Results: The estimated median overall survival was 48.9 months (95%CI 0.00-98.2) in the cohort transplanted before 2016 and not reached in the more recent years (p = 0.04) due to markedly lower non-relapse mortality (p = 0.02). The 3-year relapse incidence was low in both cohorts (11.1% and 12.5%, p > 0.99). When comparing only subgroups within the more recent cohort based on the presence or absence of total body irradiation (TBI) or the use of sequential regimens, OS and PFS were comparable. (4) Conclusion: Pretreatment with ruxolitinib, intensified conditioning, and the preferential use of haploidentical related instead of mismatched unrelated donors for patients lacking an HLA-identical donor are most likely responsible for the improved outcome after allo-HCT in MF in recent years.

Martin A, Wang Y, He M, Spellman SR, Wang T, Deeg HJ, Gupta V, Lee SJ, Bolon YT, Chanock SJ, Machiela MJ, Saber W, Gadalla SM. JAK2 V617F mutation and associated chromosomal alterations in primary and secondary myelofibrosis and post-HCT outcomes

JAK2 V617F is the most common driver mutation in primary or secondary myelofibrosis for which allogeneic hematopoietic cell transplantation (HCT) is the only curative treatment. Knowledge of the prognostic utility of JAK2 alterations in the HCT setting is limited. We identified all patients with MF who received HCT between 2000 and 2016 and had a pre-HCT blood sample (N = 973) available at the Center of International Blood and Marrow Transplant Research biorepository. PacBio sequencing and single nucleotide polymorphism-array genotyping were used to identify JAK2V617F mutation and associated mosaic chromosomal alterations (mCAs), respectively. Cox proportional hazard models were used for HCT outcome analyses. Genomic testing was complete for 924 patients with MF (634 primary MF [PMF], 135 postpolycythemia vera [PPV-MF], and 155 postessential thrombocytopenia [PET-MF]). JAK2V617F affected 562 patients (57.6% of PMF, 97% of PPV-MF, and 42.6% of PET-MF). Almost all patients with mCAs involving the JAK2 region (97.9%) were JAK2V617-positive. In PMF, JAK2V617F mutation status, allele burden, or identified mCAs were not associated with disease progression/relapse, nonrelapse mortality (NRM), or overall survival. Almost all PPV-MF were JAK2V617F-positive (97%), with no association between HCT outcomes and mutation allele burden or mCAs. In PET-MF, JAK2V617F high mutation allele burden (≥60%) was associated with excess risk of NRM, restricted to transplants received in the era of JAK inhibitors (2013-2016; hazard ratio = 7.65; 95% confidence interval = 2.10-27.82; P = .002). However, allele burden was not associated with post-HCT disease progression/relapse or survival. Our findings support the concept that HCT can mitigate the known negative effect of JAK2V617F in patients with MF, particularly for PMF and PPV-MF.

Allogeneic hematopoietic cell transplantation in patients with CALR-mutated myelofibrosis: a study of the Chronic Malignancies Working Party of EBMT

Allogeneic hematopoietic cell transplantation (allo-HCT) is curative for myelofibrosis (MF) but assessing risk-benefit in individual patients is challenging. This complexity is amplified in CALR-mutated MF patients, as they live longer with conventional treatments compared to other molecular subtypes. We analyzed outcomes of 346 CALR-mutated MF patients who underwent allo-HCT in 123 EBMT centers between 2005 and 2019. After a median follow-up of 40 months, the estimated overall survival (OS) rates at 1, 3, and 5 years were 81%, 71%, and 63%, respectively. Patients receiving busulfan-containing regimens achieved a 5-year OS rate of 71%. Non-relapse mortality (NRM) at 1, 3, and 5 years was 16%, 22%, and 26%, respectively, while the incidence of relapse/progression was 11%, 15%, and 17%, respectively. Multivariate analysis showed that older age correlated with worse OS, while primary MF and HLA mismatched transplants had a near-to-significant trend to decreased OS. Comparative analysis between CALR- and JAK2-mutated MF patients adjusting for confounding factors revealed better OS, lower NRM, lower relapse, and improved graft-versus-host disease-free and relapse-free survival (GRFS) in CALR-mutated patients. These findings confirm the improved prognosis associated with CALR mutation in allo-HCT and support molecular profiling in prognostic scoring systems to predict OS after transplantation in MF.

Allogeneic haematopoietic stem cell transplantation for myelofibrosis: prognostic indicators and the role of JAK2V617F measurable-residual disease monitoring by droplet-digital polymerase chain reaction

Relapse after allogeneic haematopoietic stem cell transplantation (HSCT) is one of the key determinants of outcome in myelofibrosis (MF) and remains an important unmet need. In this retrospective single-centre study, we evaluated 35 consecutive patients with MF receiving allogeneic HSCT. At 30 days post-HSCT, full donor chimerism was achieved in 31 patients (88.6%). The median time to neutrophil engraftment was 16.8 (10-42) days and the median time to platelet engraftment was 26 (12-245) days. Four patients (11.4%) experienced primary graft failure. With a median duration of follow-up of 33 (1-223) months, with the 5-year overall survival (OS) and progression-free survival (PFS) were 51.6% and 46.3%, respectively. Relapse after HSCT (P < 0.001), leucocyte count ≥ 18 × 109/L at HSCT (P = 0.003) and accelerated/blast phase disease at HSCT (P < 0.001) were significantly associated with worse OS. Age at HSCT ≥ 54 years (P = 0.01), mutated ETV6 (P = 0.03), leucocyte count ≥ 18 × 109/L (P = 0.02), accelerated/blast phase MF (P = 0.001), and grade 2-3 bone marrow reticulin fibrosis at 12 months post-HSCT (P = 0.002) were significantly associated with worse PFS. JAK2V617F MRD ≥ 0.047 [sensitivity 85.7%; positive predictive value (PPV) 100%; AUC 0.984; P = 0.001] at 6 months and JAK2V617F MRD ≥ 0.009 (sensitivity 100%; PPV 100%; AUC 1.0; P = 0.001) at 12 months were highly predictive of post-HSCT relapse. Inferior OS and PFS were significantly associated with detectable JAK2V617F MRD at 12 months (P = 0.003 and P = 0.0001, respectively).

Successful Outcome in Patients with Myelofibrosis Undergoing Allogeneic Donor Hematopoietic Cell Transplantation Using Reduced-Doses of Post-Transplant Cyclophosphamide: challenges and review of the literature

BACKGROUND

Engraftment and non-relapse mortality (NRM) greatly depend upon the transplant platform in patients with Myelofibrosis (MF).

OBJECTIVE

We report outcomes of 14 consecutive MF patients who received reduced doses of post-transplant Cyclophosphamide (PTCy) (60 mg/kg total dose) and tacrolimus as graft versus host disease (GVHD) prophylaxis as part of a new standardized allogeneic hematopoietic-cell transplantation (allo-HCT) protocol.

STUDY DESIGN

Median age at HCT was 59 years (range: 41-67), and median interval from diagnosis to HCT was 19 months (range: 2-114). All cases received ruxolitinib before HCT and 71% had no response. Most patients (78%) had symptomatic splenomegaly at HCT. Eighty-six percent received reduced-intensity conditioning (RIC) and most of them (64%) from an unrelated donor.

RESULTS

There were not graft failures and neutrophil and platelet recovery occurred at a median of 21 and 31 days. The cumulative incidence of grade II-IV and III-IV acute GVHD was 28.6% and 7%. The 2-year incidence of overall and moderate-severe chronic GVHD was 36% and 14%. Only 1 patient relapsed after transplant, and NRM at 100 days and 2-years was 7% and 14%. GVHD-free/relapse-free and immunosuppression free incidence at 1 year was 41%. With a median follow-up for survivors of 28 months (range:8-55), the 2-year overall survival and progression-free survival are 86% and 69%.

CONCLUSION

Reduced doses of PTCy as GVHD prophylaxis for high risk MF patients shows promising results by reducing GVHD incidence without cases of graft failure.

Hitting the brakes on accelerated and blast-phase myeloproliferative neoplasms: current and emerging concepts

The BCR-ABL-negative myeloproliferative neoplasms (MPNs) have a variable risk of progressing to accelerated- or blast-phase MPN (MPN-AP/MPN-BP), defined by the presence of 10% to 19% and more than or equal to 20% myeloid blasts in the peripheral blood or bone marrow, respectively. The molecular processes underlying the progression to MPN-AP/MPN-BP are becoming increasingly understood with the acquisition of additional mutations in epigenetic modifiers (eg, ASXL1, EZH2, TET2), TP53, the Ras pathway, or splicing factors (eg, SRSF2, U2AF1), having been described as important steps in this evolutionary process. At least partially driven by the enrichment of these high-risk molecular features, the prognosis of patients with MPN-BP remains inferior to other patients with acute myeloid leukemia, with a median overall survival of 3 to 6 months. Allogeneic hematopoietic cell transplantation remains the only potentially curative therapeutic modality, but only a minority of patients are eligible. In the absence of curative intent, therapeutic strategies or palliative treatment with hypomethylating agents as monotherapy or in combination with ruxolitinib or venetoclax can be considered. Several novel agents are in various stages of clinical development but are not available for routine use at this point, highlighting the need for ongoing research and the prioritization of clinical trial enrollment when feasible.