British Columbia Experience in Allogeneic Stem Cell Transplantation for Myelofibrosis with or without Pre-Transplant Ruxolitinib

Introduction Allogeneic stem cell transplantation (AlloHSCT) remains the only potentially curative treatment for myelofibrosis (MF). It confronts many challenges stemming from the older age of the typical patients and their age-related comorbidities, as well as disease-specific factors such as splenomegaly and hostile marrow microenvironment, which raise concerns for delayed engraftment and graft failure. Methods We performed a retrospective review of the 58 adult patients who received AlloHSCT for MF in British Columbia, Canada, in the 20-year period between January 2001 and December 2020. Data pertaining to patient demographics, disease characteristics, treatment/transplant details and clinical outcomes were gathered from the available paper and electronic records. Relapse-free survival (RFS) was defined as the time between the day of the transplant and the day of disease relapse or death from any cause. Overall survival (OS) was defined as the time between the day of the transplant and death from any cause. Patients who did not have an event during follow up were censored at the time of the last known follow up. Survival analysis was performed by Kaplan-Meier survival estimator and log-rank test, using Stata version 16.1 (Texas, USA). Results The median age of the cohort was 56 years (range 26-68), with 36% being 60 years old or older. The male to female ratio was 1.6:1. The median Karnofsky Performance Status index was 80 (range 70-100) and the median age-adjusted HCT-specific Comorbidity Index was 2 (range 0-5). The pre-transplant DIPPS plus risk category was: high in 13 patients (22%); intermediate-2 in 29 (50%); intermediate-1 in 15 (26%); and low in 1 (2%). 19/58 (33%) had a peripheral blast percentage greater than 2%. 51/58 (88%) had grade 3 fibrosis seen on the pre-AlloHSCT bone marrow biopsy. 27/57 (47%) patients were transfusion-dependent for pRBC and/or platelets. 28/54 (52%) evaluable patients had a normal karyotype and 6/54 (11%) a complex karyotype. Sixteen patients (28%) had a myeloid gene panel performed by PCR; the most commonly seen variants were ASXL1 (10 patients) and TET2 (5 patients). The median number of variants seen in a single patient was 3 (range 0-5). 42/58 (72%) patients received myeloablative conditioning before AlloHSCT. The donor type was: a volunteer unrelated donor in 54%; a matched sibling in 42%; and an alternative source (double cord or haploidentical donor) in 4%. Peripheral blood stem cells were used in 93% of the AlloHSCT. 24/58 (41%) patients received ruxolitinib pre-AlloHSCT (starting in June 2012) for a median duration of 10 months (range 1-44); 17/24 (71%) of the recipients had a clinical response to ruxolitinib but 3 had lost the response before their AlloHSCT. One patient had stopped ruxolitinib due to cytopenia. During a median follow up period of 41.7 months (range 0.5-260.7), 24/58 (41%) experienced acute graft-versus-host disease (GVHD) and 33/49 (67%) evaluable patients developed chronic GVHD. Graft failure was seen in 2 patients - one primary and the other secondary. MF relapse was seen in 13/58 (22%) after a median time of 1.1 years post-AlloHSCT (IQR 0.7-2.4). The transplant-related mortality (TRM) was 25% at 1 year and 28% at 3 years post-AlloHSCT. The most common causes of death were infection (7 patients), disease relapse (6 patients), and multiorgan failure (5 patients). Transfusion independence was achieved in 45/58 (78%) patients by day +100 and in 40/44 (90%) by 1-year post-AlloHSCT. 17/48 (35%) evaluable patients had persistent grade 3 fibrosis on their day+100 bone marrow biopsy. The estimated 1-year, 5-year and 10-year RFS rates were 66% (95% CI 52-76), 55% (95% CI 41-67) and 47% (95% CI 42-61) respectively. The estimated 1-year, 5-year and 10-year OS rates were 72% (95% CI 59-82), 63% (95% CI 49-74) and 54% (95% CI 37-68) respectively. There were no differences in RFS (p=0.40) and OS (p=0.23) between those who received ruxolitinib pre-transplant vs. those who did not. Conclusion In our cohort, approximately half the AlloHSCT recipients achieved long-term survival, many in remission (10-year OS 54%; 10-year RFS 47%). TRM was seen in 25% within the first year after AlloHSCT, with patients most commonly succumbing to infections. The graft failure rate was low at 3%. An increasing number of patients received pre-AlloHSCT ruxolitinib in the recent years but we were unable to demonstrate improved transplant outcomes with its use in this single centre cohort.

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