BackgroundSentinel-node biopsy, a minimally invasive procedure for regional melanoma staging, was evaluated in a phase 3 trial. MethodsWe evaluated outcomes in 2001 patients with primary cutaneous melanomas randomly assigned to undergo wide excision and nodal observation, with lymphadenectomy for nodal relapse (observation group), or wide excision and sentinel-node biopsy, with immediate lymphadenectomy for nodal metastases detected on biopsy (biopsy group). ResultsNo significant treatment-related difference in the 10-year melanoma-specific survival rate was seen in the overall study population (20.8% with and 79.2% without nodal metastases). Mean (SE) 10-year disease-free survival rates were significantly improved in the biopsy group, as compared with the observation group, among patients with intermediate-thickness melanomas, defined as 1.20 to 3.50 mm (71.31.8% vs. 64.72.3%; hazard ratio for recurrence or metastasis, 0.76; P=0.01), and those with thick melanomas, defined as >3.50 mm (50.74.0% vs. 40.5 +/- 4.7%; hazard ratio, 0.70; P=0.03). Among patients with intermediate-thickness melanomas, the 10-year melanoma-specific survival rate was 62.1 +/- 4.8% among those with metastasis versus 85.1 +/- 1.5% for those without metastasis (hazard ratio for death from melanoma, 3.09; P Conclusions Biopsy-based staging of intermediate-thickness or thick primary melanomas provides important prognostic information and identifies patients with nodal metastases who may benefit from immediate complete lymphadenectomy. Biopsy-based management prolongs disease-free survival for all patients and prolongs distant disease-free survival and melanoma-specific survival for patients with nodal metastases from intermediate-thickness melanomas. (Funded by the National Cancer Institute, National Institutes of Health, and the Australia and New Zealand Melanoma Trials Group; ClinicalTrials. gov number, NCT00275496.)