Study of Denileukin Diftitox in Participants With Stage IIIC and Stage IV Melanoma

This is a multicenter, open-label, dose/schedule and clinical efficacy study in participants with Stage IIIC and Stage IV melanoma. Dose-Schedules: This is a schedule, dose, and pharmacodynamic study of Denileukin diftitox in participants with Stage IIIC and Stage IV melanoma. Two arms of 40 participants each were originally planned (see below) for a total of 80 participants. Participants were randomly assigned to 1 of 2 arms: 1. 12 mcg/kg/day on Days 1 through 4 of each 21-day treatment cycle, for a total of 4 cycles (12 weeks); 2. 12 mcg/kg/day on Days 1, 8, and 15 of each 21-day treatment cycle, for a total of 4 cycles (12 weeks). Participants will be evaluated for (clinical response, safety and tolerability, and pharmacodynamic measures of ONTAK activity. An optional substudy will be conducted that will involve collection of serial tumor biopsies at study entry and Day 84 in order to assess tissue pharmacodynamic markers of ONTAK activity (Treg depletion in tumor, appearance of melanoma antigen-specific CD8+lymphocytes, and other markers of mucosal immunity and inflammatory response). Following an amendment, participants will be enrolled in Arm 1 only (expanded to a total of 55 participants) and Arm 2 was closed. According to the original design, if two responses or less were observed among 22 participants on either arm, that arm would be discontinued. Participants experiencing clinical benefit (immune-related stable disease \[irSD\], immune-related partial response \[irPR\], or immune-related complete response \[irCR\] per irRC) after 4 cycles of treatment, may continue their denileukin diftitox treatment for up to 8 cycles.