Daratumumab (DARA) maintenance or observation (OBS) after treatment with bortezomib, thalidomide and dexamethasone (VTd) with or without DARA and autologous stem cell transplant (ASCT) in patients (pts) with newly diagnosed multiple myeloma (NDMM): CASSIOPEIA Part 2.
Authors: Moreau Philippe , Sonneveld Pieter ,   for the CASSIOPEIA Study Investigators
Published: June 2021

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Background: D-VTd plus ASCT was approved for transplant-eligible (TE) NDMM based on part 1 of CASSIOPEIA. We report a prespecified interim analysis of CASSIOPEIA part 2: DARA maintenance vs OBS in pts with ≥partial response (PR) in part 1, regardless of induction/consolidation (ind/cons) treatment. Methods: CASSIOPEIA is a 2-part, randomized, open-label, phase 3 study in TE NDMM. Pts received 4 cycles ind and 2 cycles cons with D-VTd or VTd. 886 pts who achieved ≥PR were rerandomized to DARA 16 mg/kg IV Q8W for up to 2 yr (n = 442) or OBS (n = 444) until progressive disease per IMWG. Pts were stratified by ind (D-VTd vs VTd) and depth of response (minimum residual disease [MRD] status and post cons response ≥PR). Primary endpoint was progression-free survival (PFS) after second randomization. This interim analysis assessed efficacy and safety after 281 PFS events. A preplanned hierarchical procedure tested key secondary endpoints: time to progression (TTP), ≥complete response (CR), MRD negativity rates by NGS and overall survival (OS). Results: At median follow-up of 35.4 mo, median PFS was not reached (NR) with DARA and 46.7 mo with OBS (HR 0.53; 95% CI 0.42–0.68; P <0.0001). PFS advantage for DARA was consistent across most subgroups. However, a prespecified analysis showed significant interaction with ind/cons treatment arm ( P< 0.0001). PFS HR for DARA vs OBS was 0.32 (95% CI 0.23–0.46) in the VTd arm and 1.02 (0.71–1.47) in the D-VTd arm. Median TTP was NR for DARA vs 46.7 mo for OBS (HR 0.49; 95% CI 0.38–0.62; P <0.0001). More pts in the DARA vs OBS arm achieved ≥CR (72.9% vs 60.8%; OR 2.17; 95% CI 1.54–3.07; P <0.0001). MRD negativity (in ≥CR pts at 10-5) was 58.6% with DARA vs 47.1% with OBS (OR 1.80; 95% CI 1.33–2.43; P= 0.0001). Median OS was NR in either arm. Most common (≥2.5%) grade 3/4 adverse events (AEs) with DARA vs OBS were pneumonia (2.5% vs 1.4%), lymphopenia (3.6% vs 1.8%), and hypertension (3.0% vs 1.6%). Serious AEs occurred in 22.7% (DARA) vs 18.9% (OBS) of pts; the most common (≥2.5%) was pneumonia (2.5% vs 1.6%). 13 (3.0%) pts discontinued DARA due to an AE. The rate of infusion-related reactions was 54.5% (DARA-naïve pts) and 2.2% (prior DARA pts); 90% were grade 1/2.Second primary malignancies occurred in 5.5% (DARA) vs 2.7% (OBS) of pts. Conclusions: CASSIOPEIA part 2 demonstrated a clinical benefit of DARA maintenance in TE NDMM pts, with significantly longer PFS for DARA vs OBS. With current follow-up, maintenance PFS benefit appeared only in pts treated with VTd as ind/cons. Pts who received D-VTd ind/cons with or without DARA maintenance achieved similar PFS; longer follow-up is needed for PFS2 and OS. DARA significantly increased deeper response and MRD negativity rates vs OBS, and was well tolerated with no new safety signals. Clinical trial information: NCT02541383.