Higher c-MYC Expression Is Associated with Ixazomib-Lenalidomide-Dexamethasone (IRd) Progression-Free Survival (PFS) Benefit Versus Placebo-Rd: Biomarker Analysis of the Phase 3 Tourmaline-MM1 Study in Relapsed/Refractory Multiple Myeloma (RRMM)

Background

Ixazomib, the first oral proteasome inhibitor, is approved by the US FDA, in combination with Rd, for the treatment of MM patients (pts) who have received at least 1 prior therapy. Approval was based on the double-blind, placebo-controlled phase 3 TOURMALINE-MM1 study (NCT01564537) in 722 pts with RRMM (Moreau et al, N Engl J Med 2016), in which IRd showed superior PFS versus placebo-Rd (HR 0.74) at the final prespecified analysis, with limited additional toxicity. Prespecified subgroup analyses showed a consistent PFS benefit with IRd, but with a differential treatment effect according to prior therapy exposure. An exploratory study objective was to evaluate potential relationships between treatment outcomes and tumor gene expression patterns. c-MYC is a proto-oncogene that encodes a transcription factor regulating cell proliferation, growth, protein translation, metabolism, and apoptosis, and increased c-MYC expression is involved in MM pathogenesis/progression. We analyzed the impact of c-MYC expression on PFS in RRMM pts treated with IRd or placebo-Rd.

Methods

Pts with RRMM after 1-3 prior lines of therapy were randomized 1:1 to receive oral ixazomib or placebo, plus lenalidomide and dexamethasone, until disease progression or unacceptable toxicity. Randomization was stratified by number of prior therapies (1 vs 2-3), proteasome inhibitor exposure, and ISS disease stage. The primary endpoint was PFS by independent review committee assessment. Data reported here are from the final prespecified statistical analysis of PFS (median follow-up ~15 months). Bone marrow aspirate samples were collected at screening for tumor gene expression analysis. Whole transcriptome sequencing (RNAseq) of bone marrow-sorted CD138+ cells was performed using the Illumina Truseq protocol on the Illumina HiSeq platform; this generated a median of 50 million paired-end reads (100 bp length) per sample. c-MYC expression was evaluated by treatment arm and according to number of prior therapies (1 vs 2-3). PFS was analyzed in subgroups dichotomized according to median c-MYC expression (c-MYC-high/c-MYC-low).

Results

RNAseq data were available for 59% (427/722) of enrolled pts; 213 (50%) had high and 219 (50%) had low c-MYC expression (dichotomized according to the median). Impact of c-MYC expression (high vs low) on PFS, irrespective of treatment arm, was not significant (p=0.98). However, a significant treatment effect of IRd vs placebo-Rd was only seen in pts with high c-MYC expression (interaction p=0.024); in these pts (IRd: n=109; placebo-Rd: n=104) a significant PFS benefit was seen with IRd (HR 0.41; 95% CI: 0.26-0.65, p=0.00011).

Impact of c-MYC expression was then analyzed by number of prior therapies. In the overall TOURMALINE-MM1 population, per stratification, 212/213 pts in the IRd/placebo-Rd arms had 1 prior therapy, and 148/149 had 2-3 prior therapies. After median follow-up of ~15 months, median PFS in pts with 1 prior therapy was 20.6 vs 16.6 months with IRd vs placebo-Rd (HR 0.88; 95% CI: 0.65-1.20), and in pts with 2-3 prior therapies was not reached vs 12.9 months (HR 0.58; 95% CI: 0.40-0.84, p=0.0033). The level of c-MYC expression was shown to be significantly higher in pts with 2-3 prior therapies vs 1 prior therapy, with median expression of 6.94 (SD=1.71, n=177) vs 6.52 (SD=1.74, n=250) (log2 scale), t-test p-value 0.0153. In pts with 1 prior therapy, no differences in PFS were observed between pts with low c-MYC expression (HR 1; 95% CI: 0.59-1.8, p=0.934), while a prolonged PFS benefit was observed in pts with high c-MYC expression (HR 0.48; 95% CI: 0.26-0.88, p=0.0146) (Figure, A and B). In pts with 2-3 prior therapies, both the c-MYC-high and c-MYC-low pts showed improved PFS with IRd vs placebo-Rd; the difference in PFS was statistically significant only in c-MYC-high pts (HR 0.36; 95% CI: 0.18-0.72, p=0.00269) (Figure, C and D).

Conclusions

In TOURMALINE-MM1, c-MYC expression was higher in MM tumor samples from pts with 2-3 vs 1 prior therapies. The IRd regimen was active in c-MYC-high and c-MYC-low pts, but its impact on PFS vs placebo-Rd was greater in c-MYC-high pts, thus providing a potential explanation for the enhanced PFS benefit with IRd vs placebo-Rd in pts with 2-3 prior therapies. The PFS benefit with IRd in c-MYC-low pts with 2-3 prior lines suggests that, in advanced MM, further genomic alterations may also be contributing to ixazomib sensitivity.

View largeDownload slide

View largeDownload slide

Close modal