Daratumumab Effective in Combo Regimen

Adding daratumumab to bortezomib (a protease inhibitor [PI]) and dexamethasone reduces the risk of disease progression or death by 61% in patients with multiple myeloma (MM), compared with bortezomib and dexamethasone alone, according to an interim analysis of phase 3 trial results.

Related: Multiple Myeloma: Updates on Diagnosis and Management

Daratumumab is a biologic that targets CD38, a surface protein that is highly expressed across MM cells, regardless of disease stage. “CD38 is the most important tumor antigen on myeloma plasma cells,” said Antonio Palumbo, MD, University of Torino, Italy, who presented the study findings at the 2016 American Society of Clinical Oncology Annual Meeting in June. Daratumumab has more than 1 immune-mediated mechanism of action and both direct and indirect antimyeloma activity: It depletes CD38+ immunosuppressive regulatory cells and promotes T-cell expansion and activation, all while directly killing myeloma cells.

The multinational study (CASTOR) included 498 patients with MM who had received a median of 2 prior lines of therapy: bortezomib, an immunomodulatory agent, or a PI and immunomodulatory agent. Prior treatments had been unsuccessful in one-third of patients. In this study, researchers randomly assigned 251 patients to combination treatment with daratumumab.

Related: Treating Patients With Multiple Myeloma in the VA

Daratumumab significantly increased the overall response rate (83% vs 63%) and doubled rates of complete response or better (19% vs 9%). It also doubled the rates of very good partial response (59% vs 29%). The combination therapy met the primary endpoint of improved progression-free survival at a median follow-up of 7.4 months (60.7% in the combination arm, compared with 26.9%). The treatment was unblinded after meeting the primary endpoint.

The treatment benefits of the combination regimen were maintained across clinically relevant subgroups, the researchers said. The most common adverse effects were thrombocytopenia ,sensory peripheral neuropathy, anaemia, and diarrhea.

“These compelling phase 3 results demonstrate that a regimen built on daratumumab deepens clinical responses and help to underscore its potential for multiple myeloma patients who have been previously treated,” said Dr. Palumbo.

Related: A Mysterious Massive Hemorrhage

In a discussion of the study, Paul Richardson, MD, of the Dana-Farber Cancer Institute, praised the study as “outstanding” and “potentially practice changing.” However, another panel member noted that with an added cost of more than $10,000 a month, the treatment could be out of reach for many.