The Impact of Allogeneic Hematopoietic Cell Transplantation (alloHCT) on the Outcome of Poor-Risk Non-Hodgkin Lymphoma (NHL): A Retrospective Intent-to-Transplant (ITT) Analysis

Although alloHCT is an accepted salvage treatment in defined settings of poor-risk NHL, its potential benefit in these indications remains controversial because virtually all published studies are uncontrolled and restricted to patients who were actually able to undergo transplantation. Here, we aimed at assessing the impact of alloHCT by measuring its outcome from the time of donor search indication rather than from the time of transplant, thereby taking into account those patients who fail to proceed to allografting for any reason.

Study design and patients: In a single centre retrospective analysis, course and outcome of all patients with diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL) mantle cell lymphoma (MCL) and peripheral T-cell lymphoma (PTCL) who were considered as having an alloHCT indication according to accepted guidelines between 2004 and 2018 were recorded. Primary endpoint was overall survival (OS) from start of donor search. A key secondary endpoint was comparison of OS from the 3-month landmark by donor availability. Accepted donors were matched related donors (MRD), 10/10 matched unrelated donors (MUD), 9/10 compatible unrelated donors (MMUD), and mismatched related donors (MMRD), with haplo donors being used at our institution only since 2014.

Results: Altogether a donor search was initiated in 187 patients (DLBCL 32%, FL 17%, MCL 23%, PTCL 28%). Median age was 54 (19-69) years with 74% being male. Within a median time from diagnosis to search initiation of 1.1 (0.1-19) years, a median of 4 (1-9) treatment lines had been administered, including an autoHCT in 50%. 69% of the patients had active disease at the time of search initiation. Only 2 patients underwent donor search in 1^st remission (for Richter transformation and hepatosplenic T cell lymphoma, respectively). With a median follow-up of 6.2 (0.6-15.9) years, OS at 5 years after search initiation for DLBCL, FL, MCL, and PTCL was 25%, 44%, 52%, and 50%, respectively (Fig 1). 171 patients (91%) were alive at the 3-month landmark. For these, an MRD (20%), MUD (44%), MMUD (25%), or MMRD (7%) could be identified in 96% of the cases. AlloHCT was performed in 72% of all 187 patients, and in 79% of the patients alive at the 3-month landmark, with a significantly lower rate in DLBCL (69%) compared to the other entities. In patients who were actually transplanted, 5-year OS from landmark for DLBCL, FL, MCL and PTCL was 32%, 63%, 62%, and 62%, respectively, whereas only 5 of the 36 patients (14%) alive at the 3-month landmark not undergoing alloHCT for any reason survived long term. Due to the low rate of unsuccessful searches, donor vs no-donor landmark survival analyses were not possible.

Conclusions: Despite donor search now being successful in virtually all cases, 20-30% of those patients intended for alloHCT for NHL will never proceed to transplant. However, long-term OS by ITT does not seem substantially worse than alloHCT outcome observed in registry studies restricted to patients actually transplanted, with DLBCL appearing inferior to the other 3 entities. Patients surviving the 3-month landmark but not undergoing alloHCT for any reason have a poor outlook. These results may serve as benchmark for novel therapeutic options entering the NHL treatment landscape.

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