HORIZON (OP-106): An exploratory analysis of time-to-next treatment (TTNT) in patients (pts) with relapsed/refractory multiple myeloma (RRMM) who received melflufen plus dexamethasone (dex).

Abstract

e20570 Background: Melflufen is a novel peptide-drug conjugate that rapidly delivers a cytotoxic payload into tumor cells. Melflufen + dex showed efficacy and a manageable safety profile in pts with poor-risk, heavily pretreated RRMM in the phase 2 HORIZON study (Mateos et al. ASH 2019. Abs. 1883). For pts with RRMM, longer TTNT is indicative of disease stabilization and clinical benefit and is associated with lower costs (Chen et al. J Manag Care Spec Pharm. 2017). This report of TTNT after melflufen + dex from HORIZON is, to our knowledge, the first report from a trial population with such advanced RRMM. Methods: Pts with RRMM who had received ≥2 prior lines of therapy, including an IMiD and a proteasome inhibitor (PI), and were refractory to pomalidomide and/or an anti-CD38 monoclonal antibody (mAb), received melflufen 40 mg (IV on d1 of each 28-d cycle) + dex 40 mg/wk until disease progression or unacceptable toxicity. The primary endpoint was overall response rate. Secondary endpoints included progression-free survival (PFS) and safety. TTNT was defined as the time from start of melflufen + dex to first subsequent therapy. Results: Overall, 154 pts were treated (data cutoff, Oct 1, 2019); median age was 64.5 y (range, 35-86), 32% had International Staging System stage 3 disease, 38% had high-risk cytogenetics, 32% had extramedullary disease (EMD), the median number of prior therapies was 5 (range, 2-12), and 71% had triple-class refractory MM (IMiD + PI + anti-CD38 mAb). Treatment discontinuation occurred in 108 pts (70%), most commonly due to disease progression (47%) and adverse events (14%). Among 125 pts evaluable for response, with a median follow up of 15.3 mo, the median TTNT was 8.0 mo (95% CI, 7.2-8.9) and the median PFS was 4.2 mo (95% CI, 3.7-4.9). TTNT and PFS were similar in subgroups of pts with triple-class refractory MM and EMD (Table). Subsequent therapies after melflufen + dex will be presented. Conclusions: TTNT in HORIZON (median 5 prior lines) was consistent with previous reports of TTNT in pts with RRMM who received melflufen + dex or other therapies (median 2-4 prior lines) (Bringhen et al. J Clin Oncol. 2019. Abs. 8043). Melflufen + dex is being further evaluated in the phase 3 OCEAN study (NCT03151811) in pts with RRMM who are refractory to lenalidomide. Clinical trial information: NCT02963493. [Table: see text]