Phase 2 Study of the All-Oral Combination of Ixazomib Plus Cyclophosphamide and Low-Dose Dexamethasone (ICd) in Patients (Pts) with Relapsed/Refractory Multiple Myeloma (RRMM)

Background

Ixazomib, the first oral proteasome inhibitor (PI), is approved by the US FDA, in combination with lenalidomide-dexamethasone (Rd), for the treatment of pts who have received at least 1 prior therapy. Lenalidomide is a common partner agent in regimens for RRMM; however, due to increasing use of lenalidomide treatment to progression as a standard of care in the first-line setting, novel PI-based combinations without lenalidomide are needed for RRMM. Combinations of a PI, an alkylating agent, and dexamethasone have been shown to be active, with manageable side effects, in RRMM patients (e.g. VCD - bortezomib, cyclophosphamide, dexamethasone), but require SC or IV administration of the PI. The all-oral combination of ICd may offer activity, tolerability, and more convenient administration. This open-label, multicenter phase 2 study (NCT02046070) assessed the safety and efficacy of ICd in pts with RRMM.

Methods

Adult pts with RRMM after 1-3 prior lines of therapy, who had ECOG performance status 0-2, were not PI-refractory, had adequate hematologic, renal, cardiac, and hepatic function, and did not have grade ≥2 peripheral neuropathy (PN) or grade 1 PN with pain, were eligible. Pts received oral ixazomib 4.0 mg and oral cyclophosphamide 300 mg/m² on days 1, 8, and 15, plus oral dexamethasone 40 mg (20 mg for pts aged >75 yrs) on days 1, 8, 15, and 22, in 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint was overall response rate (ORR; ≥partial response [PR]); secondary endpoints included safety, pharmacokinetics (PK), complete response (CR) plus very good PR (VGPR) rate, CR rate, time to response (TTR), duration of response (DOR), and progression-free survival (PFS).

Results

78 pts were enrolled; median age was 64 yrs (40% aged >65 yrs), 53% were male, median time from initial diagnosis was 53.4 months (range, 12.9-142.7), and 24%/27% had ISS stage II/III disease at diagnosis. Median number of prior therapies was 2, including prior bortezomib, lenalidomide, and stem cell transplant (SCT) in 45 (58%), 38 (49%), and 50 (64%) pts, respectively; 17% were immunomodulatory-drug-naive. At data cut-off (June 20, 2016), pts had received a median of 12 treatment cycles (range, 1-22). A total of 51 (65%) pts had discontinued treatment, primarily due to disease progression (26 pts, 33%) and AEs (13 pts, 17%).

Overall, 92% of pts reported AEs, including 59% with grade ≥3 AEs (51%/71% in pts aged ≤65/>65 yrs), and 29% with serious AEs (30%/29%). Common AEs are listed in Table 1. AEs resulted in dose reductions of any study drug in 28 (36%) pts (28%/48% of pts aged ≤65/>65 yrs) and treatment discontinuation in 11 (14%) pts (15%/13% aged ≤65/>65 yrs). Ixazomib, cyclophosphamide, and dexamethasone were dose modified in 83%, 85%, and 87% of pts, respectively. Median ixazomib relative dose intensity was 96%. There were 3 on-study deaths: cardiac arrest, severe pulmonary edema, and cerebral hemorrhage secondary to thrombocytopenia, with the latter considered treatment-related. PK data showed that ixazomib exposures were comparable to those in pts treated with IRd in the TOURMALINE-MM1 study, suggesting no PK interaction with Cd.

ORR was 49%, including 16% CR+VGPR (Table 2); in pts with/without prior SCT, ORR was 41%/61% (15%/18% CR+VGPR). Median TTR in responding pts was 2.14 months; median DOR was not reached, with response durations of up to 17 months. After a median follow-up of 12.5 months, median PFS was not reached; 12-month PFS rate estimate was 57.5%. Subgroup analysis showed a higher ORR (68% vs 35%), a higher CR+VGPR rate (23% vs 12%), and a significant PFS improvement in pts aged >65 yrs vs pts aged ≤65 yrs (12-month PFS rate estimate 67.2% vs 50.7%; HR=0.43, p=0.028) (Figure). Although pts aged >65 yrs were less likely to have had prior SCT than those aged ≤65 yrs (22% vs 78%), this did not appear to account fully for the difference in outcomes (PFS in pts without vs with prior SCT, HR=0.82, p=0.6).

Conclusions

All-oral triplet therapy with ICd appears to have activity in RRMM pts, with a toxicity profile consistent with that seen with ixazomib in combination with Rd (Moreau, et al; N Engl J Med 2016). Preliminary best response and PFS data suggest there may be preferential benefit in elderly pts compared to younger patients (possibly related in part to more limited use of prior high-dose alkylator [melphalan] exposure associated with SCT in elderly pts) albeit with additional toxicity.

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