High-Dose Chemotherapy (HDC) with Autologous Stem-Cell Transplant (ASCT) with Consolidative Radiation Therapy (RT) for Relapsed or Refractory (R/R) Primary Mediastinal B-Cell Lymphoma (PMBCL): 20-Year Experience at MD Anderson Cancer Center (MDACC)

Background

Most PMBCL pts are cured with frontline chemoimmunotherapy ± RT. Data are scant regarding the role of HDC/ASCT for R/R PMBCL, and the benefit of RT administered peri-HDC/ASCT. Our institutional approach has focused on developing potentially more active HDC regimens, and on consideration of post-ASCT consolidation RT, especially for pts who had not achieved a CR at the time of HDC.

Methods

We retrospectively analyzed all patients (pts) with R/R PMBCL treated with HDC/ASCT at MDACC between 01/01/2000-12/31/2019. All pts underwent similar standard pre-SCT evaluation and met eligibility criteria as per our institutional guidelines. Response assessment differed over time and included CT and gallium scan (N=9) and PET/CT (N=49). Cox proportional hazards regression models evaluated the associations of the specific HDC regimen and clinical covariates of interest with EFS and OS.

Results

58 pts received HDC/ASCT with BEAM-rituximab (N=36) or rituximab/gemcitabine/busulfan/melphalan ± vorinostat (R-GemBuMel) (n=22) (Table 1). The R-GemBuMel group included more pts pretreated with >2 lines of therapy than the R-BEAM group (55% vs. 28%, p=0.025), had fewer pts in CR (41% vs. 69%, P=0.01) and more pts in PD/SD at ASCT (32% vs. 3%, P=0.01). Prior RT at a median 44 (36-48) Gy was administered to 29 pts (20 R-BEAM, 9 R-GemBuMel, P=0.27). Nineteen pts (89% not in CR at SCT) who had not previously received full doses of RT received post-SCT RT (6 after BEAM, 13 after R-GemBuMel, P<0.001) at median 40 Gy (36-48).

There were 2 treatment-related deaths in the R-BEAM arm, none in the R-GemBuMel arm. At median follow-up of 69.1 months (interquartile range, 36.5–85.2), the EFS rates were 57.6% (overall), 67.6% (R-GemBuMel) and 52.7% (R-BEAM) (Figure 1a). Their respective OS rates were 69.3%, 81.1% and 63.9% (Figure 1b).

On multivariable Cox regression analyses, R-GemBuMel (vs. R-BEAM) (HR=0.29, p=0.05), and 1 organ involved (vs. >1) (HR 0.28, p=0.009) were associated with improved EFS, whereas older age (HR= 1.08 per year above median, p=0.005), refractory disease (SD/PD) at SCT (vs. CR/PR) (HR 5.44, p=0.01) correlated with worse EFS. Likewise, R-GemBuMel (HR= 0.16, p=0.03) and 1 organ involved (HR=0.17, p=0.004) significantly resulted in improved OS, whereas older age (HR= 1.11, p=0.002), and refractory (SD/PD) disease at SCT (HR= 21.27, p=0.001) correlated with worse OS. Neither sex nor disease status (primary refractory vs. relapse) nor No. prior lines (2 vs. >2) nor pre-SCT RT nor post-SCT RT correlated significantly with EFS or OS.

Conclusions

HDC/ASCT for R/R PMBCL pts, with post-SCT RT for pts with active disease at SCT, results in favorable long-term results. R-GemBuMel ± vorinostat seems to improve EFS and OS compared to R-BEAM.