SAN DIEGO—The combination of melflufen and dexamethasone demonstrated activity in patients with multi-resistant multiple myeloma (MM) in a phase 2 trial.

Melflufen-dexamethasone produced an overall response rate of 33% in patients who had quad- or penta-refractory MM.

The combination was considered well tolerated, although 13% of patients discontinued treatment due to adverse events (AEs).

Paul Richardson, MD, of Dana-Farber Cancer Institute in Boston, Massachusetts, presented these results, from the HORIZON trial (NCT02963493), at the 2018 ASH Annual Meeting (abstract 600*).

Dr. Richardson reported results with melflufen-dexamethasone in 83 MM patients. They had a median age of 63 (range, 35-86), and 59% were male. Their median time since diagnosis was 6.5 years (range, 0.7-25) at baseline.

The patients had received a median of 5 prior lines of therapy (range, 2-13). All patients were refractory to pomalidomide or daratumumab, and 60% were refractory to both drugs. Eighty percent of patients were refractory to a monoclonal antibody, and 55% were refractory to an alkylator.

Eighty-six percent of patients were refractory to both a proteasome inhibitor and an immunomodulatory drug. Sixty percent of patients were refractory to a proteasome inhibitor, an immunomodulatory drug, and anti-CD38 therapy.

Ninety-three percent of patients were refractory to their last line of therapy. Sixty-nine percent had received a transplant, and 25% had received two transplants.

“[I]f you look at the refractoriness of these patients, 46% had used three or more prior regimens within the last 12 months before entering the trial, and I think that reflects a real challenge in these patients,” Dr. Richardson said.

Results

The patients received melflufen at 40 mg on day 1 of each 28-day cycle and dexamethasone at 40 mg weekly (20 mg for patients age 75 and older). Patients were treated until progression, consent withdrawal, or unacceptable toxicity.

The overall response rate (partial response or better) was 33%, the clinical benefit rate (minimal response or better) was 39%, and 84% of patients had stable disease or better.

Twenty seven patients responded, including one stringent complete response, nine very good partial responses, and 17 partial responses.

Five patients had a minimal response, 37 had stable disease, and 12 progressed. One patient was not evaluable, and one had data pending.

Dr. Richardson noted that melflufen-dexamethasone demonstrated activity regardless of a patient’s underlying refractory status, but serum albumin was a strong predictor of response. Specifically, patients with higher albumin levels were more likely to respond.

“We do not think it’s a mechanism-of-action issue with [melflufen], but we will be evaluating that,” Dr. Richardson said.

He went on to say that the median progression-free survival was 4.0 months overall, 6.4 months among patients with a partial response or better, and 1 month in patients with progressive disease.

Treatment-related grade 3/4 AEs occurred in 75% of patients. This included neutropenia (61%), thrombocytopenia (59%), anemia (25%), febrile neutropenia (6%), leukopenia (5%), lymphopenia (5%), infections and infestations (7%), and pneumonia (2%).

There were no treatment-related deaths. Thirteen percent of patients discontinued treatment due to AEs, most due to thrombocytopenia (8/11).

In closing, Dr. Richardson said toxicity was “generally manageable” with this treatment, which “has promising activity in multi-resistant, relapsed/refractory myeloma.”

He added that, in the phase 3 OCEAN trial (NCT03151811), researchers are comparing melflufen-dexamethasone to pomalidomide-dexamethasone in a less heavily pretreated MM population.

In the phase 1/2 ANCHOR trial (NCT03481556), researchers are testing melflufen-dexamethasone in combination with daratumumab or bortezomib.

Dr. Richardson disclosed relationships with Karyopharm Pharmaceuticals, Bristol-Myers Squibb, Janssen, Amgen, Jazz Pharmaceuticals, Takeda, Celgene, and Oncopeptides AB. The HORIZON trial is supported by Oncopeptides AB in collaboration with Precision Oncology.

*Data in the abstract differ from the presentation.

Melflufen-dex proves active in multi-resistant MM