Impact of Total Body Irradiation-Based Conditioning Regimens on Outcomes in Patients with Aggressive Mature T-Cell Lymphomas Undergoing Allogeneic Hematopoietic Cell Transplant

Background:
Mature T-cell lymphomas (MTL) are a heterogenous group of diseases representing about 10-20% of non-Hodgkin lymphomas (NHL). Standard treatment with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy yields poor long-term outcomes. Allogeneic hematopoietic cell transplantation (allo-HCT) is often considered as consolidation to improve outcomes, especially in younger patients.

Methods:
The study included adult patients (pts) with MTL who received an allo-HCT at Mayo Clinic (Rochester, Arizona and Florida) and the City of Hope Cancer Center between 2007 and 2023. Patients with cutaneous T-cell lymphomas (mycosis fungoides/Sezary syndrome) were excluded. The primary aim of the study was to evaluate long-term outcomes of allo-HCT in patients with MTL. Primary endpoints included progression-free (PFS), overall survival (OS), relapse rates, non-relapse mortality (NRM), and cumulative incidence of acute and chronic graft vs host disease (aGVHD and cGVHD).
Our second aim was to assess the impact of specific disease and transplant related factors on outcomes of allo-HCT in MTL. These included a) disease status prior to allo-HCT, b) the intensity of the conditioning regimen, c) inclusion of total body irradiation (TBI) in conditioning regimens and the use of posttransplant cyclophosphamide (PTCy) based GVHD prophylaxis

Results:
A total of 75 pts, median age 48 (22-72) years, with MTL underwent allo-HCT between 2007 and 2023 and were included in the study population. Peripheral T cell lymphoma not otherwise specified (PTCL-NOS; n=42, 56%) was the most common histology followed by angioimmunoblastic T cell lymphoma (AITL; n=13, 17%). Patients had a median of 3 (range 1-8) prior therapies and 26 (35%) pts had undergone a prior autologous HCT (auto-HCT). At the time of allo-HCT, 45 (63%) pts were in complete remission (CR) and 26 (36%) pts were in partial remission (PR). The most common donor source was HLA-matched unrelated donor (MUD; n=34, 45%) and matched related (MRD; n=24, 32%) followed by haploidentical donors (haplo; n=8, 10.7%), mistmatched unrelated donors (MMUD; n=7, 9.3%) and umbilical cord blood (UCB; n=2, 2.6%). Fifty-four pts (72%) received reduced intensity conditioning (RIC) and 20 (26.7%) received total body irradiation as part of their conditioning regimen. The median radiation dose was 1200cGy. Ten pts (13%) received PTCy-based GVHD prophylaxis.
Median follow-up of was 3 yrs (0.05-11.34). The 5-yr PFS and OS were 64.2% (53.5%-77%) and 71.3% (61.3%-82.9%), respectively; cumulative incidence of relapse and NRM were 14.5% (5.2 – 23%) and 23.5% (12.2%-33.4%), respectively. Cumulative incidence of grade II-IV and grade III-IV aGVHD at 100 days was 45.3% (32.3%-55.9%) and 9.8% (2.6%-16.5%), respectively. One-year rate of all grade cGVHD was 50.7% (36.5%-61.8%).
Patients who underwent allo-HCT while in complete remission compared to those in partial remission were noted to have superior survival with OS of 77.4% vs. 60.7% (p=0.022); no difference was noted between the two groups regarding PFS and incidence of relapse. No difference in long-term outcomes was observed based on the intensity of conditioning regimens but patients who received conditioning regimens containing TBI vs those who did not were noted to have inferior PFS of 44.9% vs 70.5% (p=0.019), with no difference in OS (58.4% vs 75.6% [p=0.059]), relapse rates (30.4% vs 10.7% [p=0.086]) and NRM (30.5% vs 20.3% [p=0.18]). Patients who received PTCy based vs. non-PTCy based GVHD prophylaxis had lower rates of chronic GVHD at 1 yrs (22% vs 56% [p=0.038]) with no difference in other outcomes.

Conclusion:
Results of our analysis show that allo-HCT represents a curative option for patients with MTL with excellent long-term outcomes. These outcomes were further improved for patients who achieved a complete remission prior to allo-HCT. The intensity of the conditioning regimen did not affect outcomes but TBI containing conditioning regimens were associated with adverse PFS. Within the limitations of a retrospective analysis and a relatively small sample, these data suggest that, a non-TBI RIC regimen, especially when combined with PTCy based GVHD prophylaxis can lead to long term disease control with limited morbidity.