Progression-Free Survival at 24 Months as A Landmark After Autologous Stem Cell Transplant in Relapsed or Refractory Diffuse Large B-cell Lymphoma

Patients with newly diagnosed diffuse large B-cell lymphoma (DLBCL) who achieve progression-free survival (PFS) at 24 months (PFS24) after immunochemotherapy (IC) have excellent overall survival (OS) comparable to that of the age- and sex-matched general population. However, a similar landmark has not been established for patients with relapsed or refractory (RR) DLBCL following frontline IC who are subsequently treated with salvage therapy followed by autologous stem cell transplantation (ASCT). To evaluate the role of PFS24 as a landmark after ASCT in patients with RR DLBCL, we identified patients with RR DLBCL after frontline R-CHOP or R-CHOP-like IC who underwent salvage therapy and ASCT at Mayo Clinic between July 2000 and December 2017 and University of Iowa between April 2003 and April 2020 from institutional lymphoma and transplantation databases. Clinical characteristics, treatment information, and outcome data were abstracted. PFS, OS, and post-ASCT relapse survival (PRS) were analyzed using Kaplan-Meier method, and cumulative incidences of relapse versus nonrelapse mortality and different causes of death were compared accounting for competing events. A total of 437 patients were identified. Median age at ASCT was 61 years (range 19-78), and 280 (64%) were male. After a median post-ASCT follow-up of 8.0 years (95% confidence interval [CI], 7.2-8.7), 215 patients had a relapse (or disease progression), 180 within 2 years and 35 after 2 years. For the entire cohort, the post-ASCT relapse rate was much higher than the nonrelapse mortality rate (48.1% versus 9.1% at 5 years). Median PFS and OS after ASCT was 2.7 and 5.4 years, respectively. Lymphoma was the primary cause of death after ASCT. In contrast, for patients who had achieved PFS24 (n = 220), rates of post-PFS24 relapse and nonrelapse mortality were similar (14.8% and 12.3% at 5 years). Median PFS and OS after achieving PFS24 was 10.0 and 11.5 years, respectively. Lymphoma-related and -unrelated death rates were similar after achieving PFS24. For all patients who had a post-ASCT relapse, median PRS was 0.7 (95% CI, 0.5-0.9) year, and late relapse (>2 versus ≤2 years after ASCT) was associated with better PRS (median 2.3 [1.7-4.8] versus 0.5 [0.3-0.7] years, P<.001). The study establishes PFS24 as an important landmark associated with post-ASCT outcomes in patients with RR DLBCL after frontline IC.