Purpose: Pivotal trial E1684 of adjuvant high-dose interferon alfa-2b (IFNalpha2b) therapy in high-risk melanoma patients demonstrated a significant relapse-free and overall survival (RFS and OS) benefit compared with observation (Obs).

Patients and methods: A prospective, randomized, three-arm, intergroup trial evaluated the efficacy of high-dose IFNalpha2b (HDI) for 1 year and low-dose IFNalpha2b (LDI) for 2 years versus Obs in high-risk (stage IIB and III) melanoma with RFS and OS end points.

Results: A total of 642 patients were enrolled (608 patients eligible), of whom a majority (75%) had nodal metastasis (50% had nodal recurrence). Unlike E1684, E1690 allowed entry of patients with T4 (> 4 mm) deep primary tumors, regardless of nodal dissection, and 25% of the patients entered onto this trial had deep primary tumors (compared with 11% in E1684). At 52 months' median follow-up, HDI demonstrated an RFS benefit exceeding that of LDI compared with Obs. The 5-year estimated RFS rates for the HDI, LDI, and Obs arms were 44%, 40%, and 35%, respectively. The hazards ratio for the intent-to-treat analysis of HDI versus Obs was 1.28 (P(2) =.05); for LDI versus Obs, it was 1.19 (P(2) =.17). By Cox analysis, the impact of HDI on RFS achieved significance (P(2) =.03). The RFS benefit was equivalent for node-negative and node-positive patients. Neither HDI nor LDI has demonstrated an OS benefit compared with Obs at this time. A major improvement in the median OS of patients in the E1690 Obs arm was noted in comparison with E1684 (6 years v 2.8 years). An analysis of salvage therapy for patients who relapsed on E1690 demonstrated that a significantly larger proportion of patients in the Obs arm received IFNalpha-containing salvage therapy compared with the HDI arm; this therapy was unavailable to patients during E1684, and patients with undissected regional nodes were not included in E1684. This study did not specify therapy at recurrence. Analysis of treatments received at recurrence demonstrated significantly more frequent use of IFNalpha2b at relapse from Obs than from HDI, which may have confounded interpretation of the survival benefit of assigned treatments in E1690.

Conclusion: The results of the intergroup E1690 trial demonstrate an RFS benefit of IFNalpha2b that is dose-dependent and significant for HDI by Cox multivariable analysis.