CHICAGO – Adding daratumumab to the current two-drug standard of care for relapsed or refractory multiple myeloma dramatically improves outcomes, according to results of an interim analysis of the phase III CASTOR trial.
When added to bortezomib and dexamethasone, the anti-CD38 antibody, which has both direct and indirect antimyeloma activity, reduced the risk of progression or death by 61%, with little increase in toxicity, investigators reported in a plenary session and press briefing at the annual meeting of the American Society of Clinical Oncology.
Dr. Antonio Palumbo
This magnitude of benefit is “unprecedented in randomized studies that compare novel treatments for relapsed, refractory multiple myeloma,” contended lead investigator Dr. Antonio Palumbo, chief of the multiple myeloma unit at the University of Torino, Italy.
“We hope this [daratumumab combination for myeloma] will be the translation of R-CHOP for lymphoma,” he added, referring to the addition of rituximab to an established backbone regimen. “Daratumumab-DVd [bortezomib-dexamethasone] might be considered today a new standard of care for relapsed and refractory multiple myeloma.”
At present, daratumumab is approved by the Food and Drug Administration for use only after patients have received at least three other therapies, Dr. Palumbo said.
“This study will open the opportunity to have a combination approach after diagnosis, therefore, at first relapse,” he commented, while noting that sufficient evidence should be obtained before using a drug for a new indication. “It’s very important to move as fast as we can this combination into the early phases of disease, where there is the major impact, even from a cost-efficacy point of view.”
The CASTOR findings add to evidence suggesting that daratumumab is synergistic with other myeloma therapies, according to invited discussant Dr. Paul G. Richardson, the R.J. Corman Professor of Medicine, Harvard Medical School, Boston, and the clinical program leader and director of clinical research at the Jerome Lipper Multiple Myeloma Center, Dana-Farber Cancer Institute, Boston.
“What I think is particularly impressive is the effect on the one-prior-line-of-treatment stratum,” he said, where the reduction in risk of progression or death was 69% with the addition of daratumumab.
Findings from the POLLUX trial, soon to be presented at another meeting, show a similar benefit when daratumumab is added to lenalidomide and dexamethasone in this setting, yielding a 63% reduction in the risk of events, according to Dr. Richardson. Additionally, other anti-CD38 antibodies and immune checkpoint inhibitors are being studied in this disease.
“I would first and foremost emphasize that this is not a zero-sum game. We need all of these drugs and all of these combinations to fight this disease,” he maintained, reviewing the many options now available. “But truly, the advent of the monoclonal antibody platform in this setting has resulted in hazard ratios that are unprecedented,” he agreed.
In CASTOR, 498 patients were randomized evenly to eight cycles of bortezomib (Velcade) plus dexamethasone, either alone or with the addition of daratumumab (Darzalex) given concurrently and then as monotherapy after completion of those cycles.
In the interim analysis, conducted at a median follow-up of about 7 months, the trial met its primary endpoint of progression-free survival: the median time to an event had not been reached with the daratumumab three-drug therapy but was 7.2 months with the standard two-drug therapy (hazard ratio, 0.39; P less than .0001). The difference translated to a more than doubling of the 1-year rate of progression-free survival (60.7% vs. 26.9%).
Benefit was generally consistent across patient subgroups stratified by disease characteristics and previous treatments, although greater impact was seen among the subgroups having earlier-stage or less heavily pretreated disease.
On the basis of these interim findings, patients in the standard therapy arm were allowed to cross over to get daratumumab, according to Dr. Palumbo.
The triple regimen was also associated with a higher overall response rate (83% vs. 63%; P less than .0001) as well as deeper responses, with a doubling in rates of both very good partial response (VGPR) or better and complete response (CR) or better.
“More patients do achieve a profound cytoreduction,” Dr. Palumbo said. “The remission duration is almost [tripled] in patients with a CR or VGPR versus patients with a minimal response or partial response.”
Data for overall survival are not yet mature, but at the time of the analysis, there was also a trend toward fewer deaths with daratumumab than without it (hazard ratio, 0.77).
“Daratumumab did not significantly increase any toxicity that was already present with the combination of bortezomib and dexamethasone,” Dr. Palumbo reported.
The three-drug regimen yielded somewhat higher rates of treatment-emergent thrombocytopenia (59% vs. 44%) and sensory peripheral neuropathy (47% vs. 38%). However, “this was mainly due to the fact that the experimental arm was longer exposed to bortezomib in comparison to the control arm that had a higher proportion of early progressions,” he explained. Additionally, the increase in thrombocytopenia did not translate into increased bleeding.