Allogeneic Stem Cell Transplantation for Relapsed / Refractory (R/R) Follicular Lymphoma (FL). a Joint Study Between the European Society for Blood and Marrow Transplantation (EBMT) and the Center for International Blood and Marrow Transplant Research (CIBMTR)

Introduction. The definitive management of R/R FL remains controversial due to various treatment options, including chemoimmunotherapy, pathway inhibitors, and autologous stem cell transplantation (auto-SCT). These options can provide prolonged progression-free survival (PFS). Allogeneic hematopoietic stem cell transplantation (allo-SCT) remains the sole curative therapy for FL. Herein, we report the long term outcome of the largest sample of allo-SCT for FL ever studied as well as the identification of patient and disease related factors that were significantly associated with treatment failure.

Patients. Eligible were adult patients with R/R FL having received a first allo-SCT between 2001 and 2011 from an HLA identical sibling donor (SIB) or a well-matched unrelated donor (MUD). Patients with transformed lymphoma were excluded from the analysis as well as planned second transplants, allotransplants from cord blood, mismatched donors, and transplants with ex vivo T cell depletion (TCD).

Results. 1567 patients met the eligibility criteria (EBMT, n = 1115; CIBMTR, n = 452). Demographics separated by data source demonstrate some differences in transplant practices between the two regions. The CIBMTR cohort had a higher proportion of MUD recipients [167 (37%) vs 252 (23%), p < 0.001], more cases with chemoresistant disease [113 (25%) vs 145 (13%), p < 0.001], less patients having received a prior auto-SCT [53 (12%) vs 403 (36%), p < 0.001], more use of myeloablative conditioning (MAC) (145 (32%) vs 220 (20%), p < 0.001) and less use of alemtuzumab in-vivo TCD [29 (6%) vs 201 (18%), p < 0.001] compared to the EBMT cohort. Median (range) follow up of survivors in months was 58 (3 - 130) and 54 (3 - 160) for CIBMTR and EBMT patients, respectively. Cumulative incidence of acute (grades II-IV) graft versus host disease (GVHD) was 20% (18-22) at 100 days and of chronic GVHD 45% (42-48) and 55% (52-58) at 1 and 3 years, respectively for the whole series; this risk was slightly but significantly reduced in the EBMT cohort. All major outcomes [non-relapse mortality (NRM), relapse/progression (R/P), overall survival (OS) and PFS] were comparable between the CIBMTR and EBMT samples (Table 1).

Multivariate analysis indicated that NRM was significantly affected by age (HR 1.04, 1.02-1.05, p < 0.0001), chemoresistant disease (HR 1.61, 1.28-2.03, p < 0.0001), >= 5 lines of prior CT (vs 3-4) (HR 1.62, 1.20-2.19, p=0.0015) and Karnofsky performance score (KPS) < 80 (HR 2.05 (1.32-3.19, p=0.0014); R/P was significantly affected by grade 3 histology (HR 1.63, 1.16-2.26, p=0.0049) and chemoresistant disease (HR 1.46 (1.07-1.97), p=0.0156); PFS by grade 3 histology (HR 1.42, 1.15-1.76, p=0.0012), chemoresistant disease (HR 1.54, 1.28-1.86, p<0.0001), >= 5 lines of prior CT (vs 3-4) (HR 1.45, 1.13-1.85, p=0.0031), MAC (HR 1.36, 1.14-1.63, p=0.0008) and KPS < 80 (HR 1.78, 1.23-2.58, p =0.0022) and OS by age (HR 1.03, 1.02-1.04, p<0.0001), grade 3 histology (HR 1.44, 1.13-1.83, p=0.0031), chemoresistant disease (HR 1.59, 1.30-1.95, p<0.0001), >= 5 lines of prior CT (vs 3-4) (HR 1.63, 1.25-2.13, p=0.0003), MAC (HR 1.42, 1.16-1.73, p=0.0006) and KPS < 80 (HR 2.23, 1.52-3.25, p<0.0001). Of note, outcomes between SIB and MUD were similar (3y OS 68% and 62%, P=0.114). Moreover a significant impact of TCD and prior auto-SCT could not be detected.

Conclusions. This study represents an example of a fruitful cooperation between two important scientific transplant societies, the EBMT and CIBMTR. Despite significant differences in patient characteristics and transplant strategies between these 2 hitherto largest samples on allo-SCT for R/R FL, long-term disease control was similar and remarkably good with an R/P risk of about only 20% at 5 years. Chemoresistant disease, higher age, multiple pretreatment lines, poor KPS, and MAC all were predictors for an adverse outcome, whereas MUD, TCD, and prior auto-SCT had no impact on any survival endpoint.