In November 2016, the US Food and Drug Administration expanded the approval of daratumumab for patients with multiple myeloma. The monoclonal antibody, which targets CD38, a protein that is highly expressed on the surface of multiple myeloma cells, was previously granted approval by the agency as a single agent for the treatment of patients who had received at least three previous therapies.
The current approval was for the use of daratumumab in two different combination regimens for the treatment of patients who have received one previous line of treatment. On the basis of improved progression-free survival (PFS), demonstrated in two randomized, open-label, phase 3 trials, daratumumab can now be used in combination with the immunomodulatory agent lenalidomide and dexamethasone, or the proteasome inhibitor bortezomib and dexamethasone, both standard therapies for the treatment of multiple myeloma.
In the POLLUX trial, 569 patients with relapsed/refractory multiple myeloma were randomized 1:1 to receive daratumumab in combination with lenalidomide-dexamethasone or lenalidomide-dexamethasone alone. The CASTOR trial randomized 498 patients with relapsed/refractory multiple myeloma 1:1 to daratumumab in combination with bortezomib-dexamethasone, or bortezomib-dexamethasone alone.
The eligibility and exclusion criteria for both trials were similar; patients had received at least one previous line of therapy, had documented progressive disease according to International Myeloma Working Group criteria, and had measurable disease on the basis of urine and/or serum assessments or serum-free, light-chain assay.
Patients with a neutrophil count of ≤1,000 cells/mm3, hemoglobin level of ≤7.5 g/dL, platelet count of <75,000 cells/mm3, creatinine clearance of ≤20 mL/min per 1.73m2 body surface area (or <30 mL/min in the POLLUX trial), alanine aminotransferase or aspartate aminotransferase level ≥2.5 times the upper limit of normal (ULN) range, bilirubin level of ≥1.5 or more times the ULN range, disease refractory to bortezomib or lenalidomide, and unacceptable side effects from bortezomib or lenalidomide, were ineligible for these studies. In addition, patients with grade 2 or higher peripheral neuropathy or neuropathic pain, were excluded from the CASTOR study.
Randomization was stratified according to International Staging System disease stage at the time of screening (stage I, II or III, with higher stage indicating more severe disease), number of previous lines of therapy (1 vs 2, or 3 vs >3), and previous receipt of lenalidomide or bortezomib.
In the CASTOR trial, patients received up to eight 21-day cycles of bortezomib, administered subcutaneously at a dose of 1.3 mg/m2 on days 1, 4, 8, and 11 of cycles 1-8, and dexamethasone, administered orally or intravenously at a dose of 20 mg on days 1, 2, 4, 5, 8, 9, 11, and 12 for a total dose of 160 mg per cycle. Daratumumab was administered at a dose of 16 mg/kg intravenously once weekly on days 1, 8, and 15 during cycles 1 to 3, once every 3 weeks on day 1 of cycles 4-8, and once every 4 weeks thereafter.
In the POLLUX trial, patients were treated in 28-day cycles. Daratumumab was administered at the same dose as in the CASTOR trial, but on days 1, 8, 15 and 22 for 8 weeks during cycles 1 and 2, every 2 weeks on days 1 and 15 for 16 weeks during cycles 3 through 7, and every 4 weeks from then onwards. Lenalidomide was administered at a dose of 25 mg orally on days 1-21 of each cycle, and dexamethasone at a dose of 20 mg before infusion and 20 mg the following day.
The combination of daratumumab with lenalidomide-dexamethasone demonstrated a substantial improvement in PFS, compared with lenalidomide-dexamethasone alone (estimated PFS not yet reached vs 18.4 months, respectively; HR, 0.37; P < .0001), representing a 63% reduction in the risk of disease progression or death. Meanwhile, there was a 61% reduction in the risk of disease progression or death for the combination of daratumumab with bortezomib-dexamethasone in the CASTOR trial (estimated PFS not yet reached vs 7.2 months; HR: 0.39; P < .0001). The PFS benefit was observed across all prespecified subgroups in both studies.
In the CASTOR trial, over a median follow-up of 7.4 months, the overall response rate (ORR) was 82.9% for the combination arm, compared with 63.2% for the bortezomib-dexamethasone arm (P < .001), with a very good partial response (VGPR) or better rate of 59.2% compared with 29.1%, and a complete response (CR) rate of 19.2% compared with 9%. In the POLLUX trial, over a median follow-up of 13.5 months, ORR was 92.9% for the combination arm, compared with 76.4% for lenalidomide-dexamethasone, with a VGPR or better rate of 75.8% versus 44% and a CR rate of 43.1% versus 19.2%.
Overall, the safety profile for both combinations was consistent with what is usually observed with daratumumab monotherapy and lenalidomide-dexamethasone or bortezomib-dexamethasone combinations. The most frequently reported adverse events (AEs) were similar in both studies and included infusion reactions, diarrhea, and upper respiratory tract infection. In the POLLUX trial they also included nausea, fatigue, pyrexia, muscle spasm, cough, and dyspnea, whereas in the CASTOR trial patients also frequently experienced peripheral edema.
The most common grade 3/4 AEs in both trials were neutropenia (51.9% vs 37% in the POLLUX trial and 12.8 vs 4.2% in the CASTOR trial), thrombocytopenia (12.7% vs 13.5% and 45.3% vs 32.9%, respectively), and anemia (12.4% vs 19.6% and 14.4% vs 16%, respectively). The percentage of patients who discontinued treatment due to AEs was similar in both groups across the two studies; in the CASTOR trial discontinuations resulted most commonly from peripheral sensory neuropathy and pneumonia, while in the POLLUX trial, from pneumonia, pulmonary embolism and deterioration in general physical health.
The recommended dose for daratumumab in both combination regimens is 16 mg/kg intravenously, calculated on actual body weight. The dosing schedules begin with weekly administration during weeks 1-8 (when used in combination with lenalidomide-dexamethasone) and weeks 1-9 (for use with the bortezomib-dexamethasone combination), decreasing to every 2 weeks between weeks 9 and 24 or 10 and 24, respectively, and progressing to every 4 weeks from week 25 onward until disease progression and unacceptable toxicity.
Daratumumab is marketed as Darzalex by Janssen Biotech Inc. Neutropenia and thrombocytopenia have been added to the list of warnings and precautions for the prescribing information for these new indications. Complete blood cell count should be monitored periodically during treatment and daratumumab administration delayed to allow recovery of neutrophils or platelets. Supportive care with growth factors or transfusion should be considered in the event of neutropenia or thrombocytopenia, respectively.