LBA8506 Background: Adjuvant therapy with low-dose adjuvant interferon alfa-2b (IFN) as well as with pegylated interferon alfa-2b (PEG-IFN) were both shown to be superior to observation in melanoma (M) patients (pts) without macro-metastatic nodes. However, the two strategies have never been assessed head to head. Weekly injection of PEG-IFN facilitates a longer duration of treatment which may be critical for benefit. We thus compared adjuvant therapy of flat low-dose PEG-IFN (36 months) versus low-dose IFN (18 months) in intermediate-risk M pts without macro-metastatic nodes. Methods: In this multicenter, open-label, prospective randomized phase III trial, pts with resected M ≥ 1.5 mm in thickness and without clinically detectable nodes were randomized either to IFN (3 MU subcutaneously [sc] 3 times a week for 18 months) or to PEG-IFN (100 mcg sc once weekly for 36 months). Sentinel node procedure (SNP) was not a standard in 2003 and thus was optional. Approach was consistent by center. Randomization was stratified for centers and SNP procedure. Primary endpoint was relapse-free survival (RFS), and secondary were distant metastasis-free survival (DMFS), overall survival (OS), and grade 3-4 severe adverse events (SAE). Sample size (890 pts) was calculated to detect a 10% difference (power >80%, type I error of 5%, 2-sided) for RFS. Analysis describes 5-year probability of survival. Comparisons were done by intent-to-treat using Cox proportional models. Results: Of 898 pts enrolled, 896 (443 PEG vs 453 IFN) were eligible for evaluation after a median follow-up of 4.7 years. SLNB was performed in 68.2% of pts. Neither RFS (PEG-IFN 66.2% vs IFN 64.8%, p=0.43; HR, 0.91; 95% CI, 0.73 to 1.15) nor DMFS (71.3% vs 72.6%, p=0.86; HR, 1.02; 95% CI, 0.80 to 1.32) or OS (77.0% vs 78.4%, p=0.55; HR, 1.09; 95% CI, 0.82 to 1.45) showed statistical difference. There was an excess of SAE grade 3-4 in PEG-IFN arm (44.6% vs 26.6% in the first 18 months) which impacted on median duration of treatment (17.8 months in IFN arm; 19.2 in PEG-IFN arm, with only 28% completing 36 months treatment). Conclusions: Flat low-dose PEG-IFN did not show superiority over conventional low dose IFN. Attempts to increase benefit by prolonging treatment with PEG-IFN over 3 years were hampered by a high rate of treatment discontinuation possibly linked to SAEs with PEG-IFN. [Table: see text]

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