PS1382 DEEPENING RESPONSES SEEN WITH IXAZOMIB MAINTENANCE POST‐AUTOLOGOUS STEM CELL TRANSPLANTATION (ASCT) ARE ASSOCIATED WITH PROLONGED PROGRESSION‐FREE SURVIVAL – ANALYSIS FROM THE TOURMALINE‐MM3 STUDY
Authors: Goldschmidt H. , Dimopoulos M.A. , Rajkumar S.V. , Weisel K.C. , Moreau P. , Chng W.‐J. , Mikala G. , Cavo M. , Ramasamy K. , Suryanarayan K. , Teng Z. , Labotka R. , Mateos M.V. 
Published: June 2019

Background:

Deepened response has been associated with prolonged progression‐free (PFS) and overall survival in multiple myeloma, including in the maintenance therapy setting. In the Myeloma XI trial, post‐ASCT maintenance with lenalidomide vs observation resulted in improved responses in 15.8% vs 11.0% of patients (pts) and a median PFS of 56.9 vs 30.1 months (Jackson et al, ASH 2017). In the phase 3, double‐blind, placebo‐controlled TOURMALINE‐MM3 study (NCT02181413), post‐ASCT maintenance therapy with the oral proteasome inhibitor (PI) ixazomib vs placebo resulted in a 39% improvement in PFS (median 26.5 vs 21.3 months; HR 0.72; 95% CI: 0.58–0.89; p = 0.002), with a favorable safety profile (Dimopoulos et al, Lancet 2019). We report improvements in depth of response and the impact on outcomes in TOURMALINE‐MM3.

Aims:

To evaluate the rates and timing of response improvement during ixazomib vs placebo maintenance and the impact on PFS in TOURMALINE‐MM3.

Methods:

Pts who had achieved ≥partial response (PR) to induction therapy with a PI and/or immunomodulatory drug followed by single ASCT were randomized 3:2 to receive ixazomib (N = 395) or placebo (N = 261) on day 1, 8, and 15 of 28‐d cycles for up to 2 years or until progressive disease or unacceptable toxicity. Randomization was stratified by induction regimen, pre‐induction ISS stage, and post‐ASCT response (complete response [CR] or very good PR [VGPR] vs PR). Ixazomib dose was 3 mg in cycles 1–4 and 4 mg from cycle 5 if tolerated in cycles 1–4. Minimal residual disease (MRD) was assessed at screening by flow cytometry (10–5 sensitivity). The primary endpoint was PFS per independent review committee (IRC). Other endpoints included rate of response improvement in pts enrolled in VGPR or PR.

Results:

At study entry, 60 (15%), 213 (54%), and 89 (23%) pts in the ixazomib arm and 54 (21%), 152 (58%), and 35 (13%) in the placebo arm had CR, VGPR, and PR, respectively, by IRC. Deepening responses were seen in 139/302 (46%) ixazomib vs 60/187 (32%) placebo pts with VGPR/PR at enrollment (relative risk [RR] 1.41, 95% CI 1.1–1.8, p = 0.004), including 92/213 (43%) vs 48/152 (32%) VGPR to CR (RR 1.37, p = 0.025) and 47/89 (53%) vs 12/35 (34%) PR to VGPR/CR (RR 1.54, p = 0.063). On Kaplan‐Meier analysis of time to best deepened response in VGPR/PR pts (Figure), 24‐month rates of deepening response were 54.2% vs 41.4%, and there was a 38.4% improvement in the chance of deepening response over time with ixazomib vs placebo (HR 1.384, p = 0.034). A pooled analysis across arms among pts enrolled in VGPR/PR showed that deepening response vs no improvement was associated with prolonged PFS (median not reached vs 15.9 months; HR 0.245, 95% CI 0.184–0.325, p < 0.0001). Analysis by treatment arm showed that, in VGPR/PR pts with deepening response, 24‐month PFS rates were 77.4% vs 68.3% with ixazomib vs placebo (medians not reached; HR 0.875; 12.5% risk reduction; 95% CI 0.52–1.47; p = 0.615); in VGPR/PR pts without deepening response 24‐month PFS rates were 33.4% vs 23.6% (median 17.9 vs 14.1 months; HR 0.780; 22% risk reduction; 95% CI 0.59–1.03; p = 0.080). Baseline MRD status was a strong predictor of deepening response; deepening responses were seen in 63% (78/124) vs 32% (94/293) of MRD‐ vs MRD+ pts enrolled in VGPR/PR.

Summary/Conclusion:

Post‐ASCT maintenance with ixazomib resulted in a significantly higher rate of deepening response vs placebo; deepening response was associated with prolonged PFS. Ixazomib resulted in non‐significant PFS benefit vs placebo in VGPR/PR pts with and without deepening response; prolonged follow‐up would be needed to confirm these results.

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