BOSTON – Melflufen plus dexamethasone is active in patients with relapsed/refractory multiple myeloma, whether or not they have extramedullary disease (EMD), a phase 2 trial suggests.
In the HORIZON trial, melflufen-dexamethasone produced an overall response rate of 23% in patients with EMD and 27% in those without EMD.
, of Harvard Medical School and the Dana-Farber Cancer Institute, both in Boston, presented these results as a late-breaking abstract at the International Myeloma Workshop, held by the International Myeloma Society.
As of July 30, 2019, 136 patients had been treated on the HORIZON. The trial is enrolling patients with relapsed/refractory multiple myeloma refractory to pomalidomide, an anti-CD38 monoclonal antibody (mAb), or both. The patients must have received at least two prior lines of therapy, including a proteasome inhibitor (PI) and an immunomodulatory agent (IMiD).
Dr. Richardson presented results for 130 patients, 44 with EMD and 86 without it. The median age at baseline was 64 years in the EMD and non-EMD groups (overall range, 35-86 years). More than half of patients had high-risk cytogenetics (52% in the EMD group and 57% in the non-EMD group).
The median number of prior therapies was five in both the EMD and non-EMD groups. Most patients had received at least one prior transplant (73% in the EMD group and 69% in the non-EMD group). Most patients in both groups were refractory to an anti-CD38 mAb (93% EMD and 72% non-EMD); an IMiD and a PI (93% EMD and 90% non-EMD); an IMiD, a PI, and an anti-CD38 mAb (91% EMD and 63% non-EMD); and their last therapy (100% EMD and 95% non-EMD).
Dr. Richardson pointed out that the incidence of EMD in this trial is higher than has been reported previously. Of the 44 EMD patients, 26 had soft-tissue EMD, and 18 had bone-related EMD. Five patients had CNS involvement.
Another key finding, according to Dr. Richardson, was that EMD appeared to be associated with prior anti-CD38 therapy. Specifically, 40% of patients exposed to an anti-CD38 mAb had EMD, compared with 11% of patients who had not received an anti-CD38 mAb (P = .01).
“I don’t for a minute want to say that CD38-targeted therapy engenders extramedullary disease,” Dr. Richardson said. “I think what we can say, though, is that, once CD38 treatment fails a patient, extramedullary disease … is a very real challenge. Therefore, we need rationally targeted approaches, ideally in combination, to meet that challenge.”
The overall response rate was similar for EMD and non-EMD patients – 23% and 27%, respectively. The median duration of response was 3.4 months in the EMD patients and 4.4 months in the non-EMD group. The clinical benefit rate was 30% and 45%, respectively.
In the EMD group, the overall response rate was 19% in patients with soft-tissue EMD and 28% in bone-related EMD. None of the patients with CNS disease responded.
The median progression-free survival was 2.9 months for patients with EMD and 4.6 months for those without EMD. The median overall survival was 5.8 month and 11.6 months, respectively.
The median overall survival was 18.5 months in EMD responders and 17.2 months in non-EMD responders. The median overall survival was 5.1 months in EMD nonresponders and 8.5 months in non-EMD nonresponders.
In all, 54% of patients received subsequent therapy. There were no significant differences in outcomes between EMD and non-EMD patients.
The safety profiles were similar for EMD and non-EMD patients, Dr. Richardson said. Melflufen-dexamethasone was considered well tolerated overall, and there were no treatment-related deaths.
The most common treatment-emergent adverse events (grade 3 and 4, respectively) were thrombocytopenia (22% and 46%), neutropenia (32% and 35%), anemia (35% and 1%), white blood cell count decrease (10% and 7%), and pneumonia (7% and 1%).
This trial is sponsored by Oncopeptides. Dr. Richardson reported an advisory role and research funding from Oncopeptides.
SOURCE: Richardson PG et al. IMW 2019, .