Salvage Autologous Stem Cell Transplantation in Multiple Myeloma: Investigating the Impact of Pre-Transplant Therapy

Introduction

Autologous stem cell transplantation (ASCT) plays a central role in the treatment of multiple myeloma (MM), even in the era of novel therapies (Gonsalves et al, 2018). Given the efficacy of the latter, as well as for logistical reasons, many patients opt to store their stem cells and delay ASCT until the time of progression. Delayed transplant does not appear to affect overall survival (OS) (Attal et al, 2017). However, in the "salvage" setting, the impact of treatment with additional chemotherapy prior to ASCT is unknown. One study, albeit in the front-line, suggested that in patients achieving less than a partial response (PR), additional induction prior to ASCT did not improve survival (Vij et al, 2015). The present study investigates the role of induction therapy prior to salvage ASCT.

Methods

We identified 380 patients who underwent ASCT >12 months after being diagnosed with MM from January 1, 2006 to July 1, 2017 at Mayo Clinic Rochester. 121 had a delayed ASCT, but no International Myeloma Working Group (IMWG) progression prior to ASCT and were excluded. Another 17 patients achieved less than PR prior to ASCT, thus were deemed primary refractory and excluded. Finally, 8 patients were excluded because they received a planned tandem ASCT. Thus, 234 patients were included in the present study, which was approved by the Mayo Clinic Institutional Review Board, in accordance with the Declaration of Helsinki.

We refer to the time of progression prior to ASCT, after which we examined the use of pre-ASCT therapy, as T₀ to avoid confusion. Time to next therapy (TNT) was defined as the time from ASCT (stem cell infusion, Day +0) to the initiation of a new therapy, not including planned consolidation or maintenance. Patients who were alive and had not received any new therapies, or died before receiving another therapy were censored at the time of last follow up, as of May 15, 2018. OS was defined as the time from Day +0 to death from any cause, with living patients censored at the time of last follow-up. TNT and OS were estimated using the Kaplan-Meier method and compared using the log-rank test. A Cox proportional hazard model was used for univariate and multivariate analysis. High-risk cytogenetics were defined as del(17/17p), t(4;14), t(14;16), and t(14;20). The Mann-Whitney U test and Fisher's Exact test were used to compare continuous and categorical variables, respectively. Statistical analysis was completed using JMP 13.0 (SAS Institute Inc., Cary, NC, USA).

Results

Of the 234 patients who underwent salvage ASCT, 188 were treated with additional chemotherapy after T₀ (hereafter referred to as "pre-ASCT induction"), whereas 46 patients went directly to ASCT. Baseline characteristics were comparable, however more patients in the pre-ASCT induction group had >1 progression prior to ASCT (28% vs. 9%, p= .0065) and had a trend towards a shorter duration of response (DOR) prior to T₀ (14.7 vs. 18.5 months, p= .12). Intuitively, the pre-ASCT induction group had a longer time from T₀ to ASCT (5.3 vs. 2.3 months, p< .0001).

The median TNT for the entire cohort of 234 patients from Day +0 was 17.2 months (95% CI, 14.8-19.7); median OS was 50.4 months (95% CI, 43.3-60.7). TNT and OS were comparable between the two treatment groups (Figure 1). After adjusting for other significant prognostic factors, such as DOR prior to T₀ and the presence of high risk cytogenetics, treatment with pre-ASCT induction did not significantly affect TNT or OS (Table 1).

However, among the 188 patients treated with pre-ASCT induction, the subsequent depth of response prior to ASCT significantly affected TNT (Figure 2A) and OS (Figure 2B). TNT at 1-year post ASCT was 79.2% for patients achieving a ≥VGPR, 62.1% in those who achieved a PR or stable disease, and 45.7% for patients who had relapsed/refractory MM at the time of ASCT or received >2 lines of pre-ASCT therapy (p= .0003). Interestingly, the time from diagnosis to T₀ was comparable between these 3 groups (27 vs. 28 vs. 26 months, respectively, p= .26).

Conclusions

Many patients with MM do not undergo ASCT until disease progression. In our cohort of 234 patients who underwent salvage ASCT, outcomes were similar whether patients received pre-ASCT induction or not. However, among the 188 patients treated with pre-ASCT induction, deeper responses correlated with significantly longer TNT and OS after ASCT. Further research into the role of chemotherapy prior to delayed ASCT in the era of novel agents is warranted.

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