This multicenter, open-label study will assess the safety and pharmacokinetics of DEDN6526A in patients with metastatic or unresectable melanoma. Cohorts of patients will receive escalating doses of DEDN6526A by intravenous infusion on Day 1 of each 21-day cycle. In the absence of disease progression or unacceptable toxicity, patients may continue to receive DEDN6552A for up to 17 cycles (1 year).