COPENHAGEN (FRONTLINE MEDICAL NEWS) In a classic case of clinical sibling rivalry, results of the POLLUX trial support the benefits of adding daratumumab to lenalidomide and dexamethasone in patients with relapsed/refractory multiple myeloma, echoing results reported a few days earlier by investigators in the twin (and archly named) CASTOR trial

Among 569 patients with relapsed/refractory multiple myeloma, the addition of the anti-CD38 monoclonal antibody daratumumab (Darzalex) to lenalidomide (Revlimid) and dexamethasone was associated with a 63% reduction in the risk of disease progress or death, compared with len-dex alone, reported Dr. Meletios A Dimopoulos of the National and Kapodistrian University of Athens.

With daratumumab and len-dex, “there is the highest-ever response rate seen in relapsed or refractory myeloma; 93% of the patients achieved at least a partial response, and more importantly, 43% of the patients achieved a complete response,” he said at a briefing prior to his presentation of the data at the annual congress of the European Hematology Association.

“The addition of daratumumab to lenalidomide and dexamethasone induces deep and durable responses. Data indicate that we can achieve minimal residual disease negativity status in a significant number of patients,” he added.

The trial was halted on May 20, 2016, after a preplanned interim analysis showed a significant improvement in the primary endpoint of a progression-free survival, compared with len-dex alone.

Dizygotic twins

Like their mythologic namesakes, who were twin sons from different fathers, the CASTOR and POLLUX trials differed somewhat in the patient populations treated and in trial design. The CASTOR trial is looking at the addition of daratumumab to bortezomib (Velcade) and dexamethasone, and excludes patients resistant to bortezomib. The POLLUX trial includes bortezomib-resistant patients, but excludes lenalidomide-resistant patients.

In addition, in CASTOR, patients were treated with the assigned regimen for a specified number of courses, followed by daratumumab maintenance, whereas patients in both arms in POLLUX continued on their assigned therapy until disease progression or unacceptable toxicity occurred.

POLLUX was a multicenter, randomized, open-label phase III trial in patients with relapsed/refractory multiple myeloma following one or more prior lines of therapy. They were randomized on a 1:1 basis to either len-dex (283 patients) or len-dex plus intravenous daratumumab at a dose of 16 mg/kg once a week during treatment cycles 1 and 2, every 2 weeks during cycles 3-6, and once only on day 1 of subsequent cycles.

After a median follow-up of 13.5 months, the median progression-free survival for patients treated with len-dex alone was 18.4 months, but the median was not yet reached among patients treated with daratumumab. The difference translated into a hazard ratio for progression-free survival with daratumumab of 0.37 (P less than .0001).

In addition, the antibody was associated with a significantly better overall response rate (93% for daratumumab vs. 76% for len-dex only; P less than .0001), as well as better rates of complete responses (43% vs. 19%, respectively; P less than .0001), and very good partial responses or better (76% vs. 44%, P less than .0001).

The combination was generally well tolerated, with adverse events consistent with the known safety profile of len-dex. Infusion reactions with daratumumab were generally mild, and tended to occur during the first infusion, Dr. Dimopoulos said.

Dr. Anton Hagenbeek, professor of hematology at the University of Amsterdam (the Netherlands), who moderated the briefing, commented that the progression-free survival curves with daratumumab appeared to plateau, and asked whether any patients in the trial could be considered to have been “cured.”

Dr. Dimopoulos replied that “although we believe that in the relapsed setting of myeloma, it is unlikely to achieve the cure rate, we are optimistic that there will be a sizable number of patients that will remain without progression for many months. Already from single-agent daratumumab where this patient population is far more heavily pretreated, there are patients who are without progression for several years.”

Dr. Dimopoulos has previously disclosed honoraria from Janssen, maker of daratumumab. Dr. Hagenbeek disclosed serving on an advisory board for Takeda, maker of bortezomib.