A randomized controlled trial compared surgical excision margins of 2 cm versus 4 cm for patients with cutaneous melanomas thicker than 2 mm. The trial involved 936 patients across multiple centers who were allocated to the 2 cm or 4 cm margin groups. After 6-7 years of follow up, there were no differences in overall survival or recurrence free survival between the groups. The results suggest clinicians can safely use a 2 cm excision margin for thick melanomas (>2mm).