Patients

Patients who were 18 years of age or older were eligible for enrollment if they had histologically confirmed, unresectable stage III or IV melanoma and had received no more than one previous systemic therapy for advanced disease. Known BRAF V600 mutational status was required; previous BRAF inhibitor therapy was not required for patients with normal lactate dehydrogenase levels and no clinically significant tumor-related symptoms or evidence of rapidly progressive disease. Other key eligibility criteria included an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 (on a 5-point scale, with higher scores indicating greater disability) and provision of a tumor sample adequate for assessing PD-L1 expression. Excluded from the study were patients who had received previous therapy with CTLA-4, PD-1, or PD-L1 inhibitors and those who had ocular melanoma, active brain metastases, or a history of serious autoimmune disease.

Study Design and Treatment

Patients were randomly assigned in a 1:1:1 ratio to receive pembrolizumab at a dose of 10 mg per kilogram of body weight either every 2 weeks or every 3 weeks or four cycles of ipilimumab at a dose of 3 mg per kilogram every 3 weeks. Randomization was stratified according to ECOG performance status (0 versus 1), line of therapy (first versus second), and PD-L1 expression (positive versus negative).

Pembrolizumab was administered intravenously during a 30-minute period and continued until disease progression, the onset of unacceptable side effects, an investigator's decision to discontinue treatment, withdrawal of patient consent, or 24 months of therapy. Patients with confirmed complete response who received pembrolizumab for at least 6 months could discontinue therapy after receiving at least two doses beyond the determination of complete response. Ipilimumab was administered intravenously during a 90-minute period and continued for four cycles or until disease progression, the onset of unacceptable side effects, an investigator's decision to discontinue treatment, or withdrawal of patient consent. After initial evidence of radiologic progression, patients whose condition was clinically stable could continue to receive study treatment until imaging that was performed approximately 4 weeks later confirmed progression. (Details regarding the management of treatment decisions are provided in the protocol, available with the full text of this article at NEJM.org.)

Study Assessments

PD-L1 status was assessed in archival or newly obtained tumor samples by means of immunohistochemical analysis with the use of the 22C3 antibody (Merck) at a central laboratory before randomization. Positivity was defined as membranous PD-L1 staining in at least 1% of tumor cells. Response was assessed at week 12 and every 6 weeks thereafter according to Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1,18 on the basis of central radiologic review and immune-related response criteria19 by investigator review. RECIST was used for the primary assessment of efficacy, whereas immune-related response criteria were used for managing treatment. Survival was assessed every 3 months after the discontinuation of a study drug. Adverse events, laboratory values, and vital signs were assessed regularly and graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0.

End Points

Primary end points were progression-free survival (defined as the time from randomization to documented disease progression according to RECIST or death from any cause) and overall survival (defined as the time from randomization to death from any cause). Secondary end points included the objective response rate (defined as the percentage of patients with complete or partial response according to RECIST), the duration of response (defined as the time from the first documented response to radiologic progression according to RECIST), and safety. Efficacy was assessed in the intention-to-treat population, with all patients included in the treatment group to which they were randomly assigned. Safety was assessed in the as-treated population, which was defined as all patients who underwent randomization and who received at least one dose of a study drug.

Study Oversight

The original protocol and all amendments were approved by the relevant institutional review board or independent ethics committee at each study center. The study was conducted in accordance with the protocol, Good Clinical Practice guidelines, and the provisions of the Declaration of Helsinki. All patients provided written informed consent.

KEYNOTE-006 was designed by representatives of the study sponsor, Merck Sharp & Dohme, a subsidiary of Merck, and the academic advisors. An external data and safety monitoring committee oversaw the study. (Members of the committee are listed in the Supplementary Appendix, available at NEJM.org.) All data were collected by investigators and associated site personnel, analyzed by statisticians employed by the sponsor, and interpreted by the authors, including those from the sponsor. The corresponding and senior authors wrote the first draft of the manuscript. Assistance in manuscript preparation was provided by a science writer paid by the sponsor. All authors participated in reviewing and editing the manuscript, approved the submitted draft, had full access to the data used to write the manuscript and vouch for their accuracy, and attest that the study was conducted in accordance with the protocol.

Statistical Analysis

We used the Kaplan–Meier method to calculate estimates of progression-free and overall survival. Data for patients who did not have disease progression or who were lost to follow-up were censored at the time of last tumor assessment for progression-free survival. Treatment differences for progression-free and overall survival were assessed by means of the stratified log-rank test. Hazard ratios and associated 95% confidence intervals were assessed with the use of a stratified Cox proportional-hazards model with Efron's method of handling ties. We compared response rates in the study groups using the stratified Miettinen and Nurminen method.

The protocol specified the performance of two interim analyses (as summarized in Table S1 in the Supplementary Appendix). The first analysis was to be performed after at least 260 patients had disease progression or died in all study groups and all patients had been followed for at least 6 months. The primary objective of this analysis was to evaluate the superiority of either pembrolizumab regimen over ipilimumab for progression-free survival at a one-sided alpha level of 0.002. At the first interim analysis, overall survival was evaluated at a one-sided alpha level of 0.00002 to have a negligible effect on the overall type I error rate to preserve the alpha level for the second interim and final analyses. The second interim analysis, in which the primary objective was to evaluate the superiority of either pembrolizumab regimen over ipilimumab for overall survival at a one-sided alpha level of 0.005 with the use of the Hochberg step-up procedure, was to be performed after at least 290 patients had died in all the study groups and all patients had been followed for at least 9 months or when the minimum follow-up duration was 12 months, whichever occurred first.

The first interim analysis, with a data cutoff of September 3, 2014, was conducted by an independent statistician who was aware of study-group assignments. After the data and safety monitoring committee reviewed the results, they recommended continuing the study as planned and unblinding the results to select representatives of the study sponsor for regulatory purposes. The second interim analysis, with a data cutoff of March 3, 2015, was conducted in an unblinded manner by a statistician employed by the sponsor. After reviewing the results of the second interim analysis, the data and safety monitoring committee recommended that the study results be unblinded and pembrolizumab be made available to patients with disease progression in the ipilimumab group. Final overall survival analysis will be performed after at least 435 deaths have occurred in all the study groups or when all patients have been followed for at least 21 months. All data presented here are from the first interim analysis, except those for overall survival, which are from the second interim analysis.