Depth of Response to ≥VGPR at Completion of Induction Influences Outcome Post ASCT, on Behalf of the Tunisian Myeloma Study Group

Background: High dose Melphalan (HDM) and autologous stem cell transplantation (ASCT) is a standard care for Myeloma ≤ 65 years. Studies have demonstrated that depth of response prior to ASCT does not impact outcome post ASCT, e.g. solely depth of response post ASCT matters. However, with improving induction regimens, the questions remains whether patients achieving a deeper response at completion of induction would not perform better post ASCT.

ASCT can only be performed in Tunisia if newly diagnosed Multiple Myeloma (NDMM) achieves at least PR; we therefore sought to report the national Tunisian experience.

Patients and Methods: NDMM aged ≤65 years received three cycles of Thalidomide (200mg daily) and Dexamethasone, followed by HDM and ASCT.52% received maintenance therapy for 12 months with Thalidomide, from 3 months post transplantation. Non responders to TD induction were salvaged with Lenalidomide or Bortezomib-based regimen. The response was assessed based on IMWG response criteria. The study is performed in ITT.

Results: 202 consecutive pts were included between April 2012 and December 2014. The median age was 56 yrs (range, 25-65), sex ratio was 1.R-ISS stage was 3 in 27.5%. 21% had high risk cytogenetic (by Conventional karyotyping and FISH). Renal failure was observed in 17%. ORR after induction was 71% with 12% CR, 17% VGPR. 22% failed to obtain PR following TD induction, and 51% of whom received salvage induction therapy (ST) with 72% that further reached ≥PR after ST. Overall, 141 pts (70%) underwent ASCT, 121 of whom had evidence of chemo-sensitive MM at completion of induction. 16% were transplanted in CR, 22% in VGPR and 62% in PR.

At 3 months post-ASCT, the ORR in induction chemo-sensitive MM was 89%: 36% CR, 20% VGPR, and 33% PR. With a median follow-up post-ASCT of 27 months, the OS, PFS and EFS at 27 months were 82%, 60.5% and 56%, respectively. Maintenance treatment was significantly associated with longer PFS only in MM who did not achieve CR (29 versus 9 months, p=0.004). MM with improved response post-ASCT had a significantly longer PFS (39 versus 21 months, p=0.003) and EFS (39 versus 20 months, p=0.002). Importantly, achieving CR before (p=0.03) and after ASCT (p<0.0001) was also predictive for prolonged EFS. Early relapses/progressions (less than 18 months) was the sole predictive factor of adverse OS in our study (p=0.01).

In multivariate analysis, ISS stage 3 was the sole independent predictor of induction failure (p=0.003). Importantly, predictive factors of achievement of CR post-ASCT comprised absence of delay farther to 4 months from completion of induction (p=0.006; OR = 4.54) and achievement of at least VGPR status before transplant (p=0,001; OR = 4.09).

Conclusion: Achievement of at least VGPR at completion of induction improved response after ASCT and consequently influenced the post-ASCT outcome. Therefore, depth of response matters before and after ASCT, and validates in some extent the concept of induction salvage therapy prior to ASCT for patient not reaching response.