Melanoma With an Unknown Primary in an Asymptomatic Elderly Male With Unilateral Lymphadenopathy

Melanoma with an unknown primary (MUP) is an uncommon metastatic melanoma without an obvious primary site. MUP has a higher prevalence in men in their fifth decade of life. The pathogenesis of MUP is still unknown but several hypotheses have been proposed including the predominant regression theory, occult cutaneous, or visceral location, or by the presence of ectopic melanocytes. Proper physical examination, imaging, and histopathological review are needed to diagnose MUP. Patients with MUP must be aggressively treated and monitored for recurrence. We present a case of MUP occurring in an asymptomatic 61-year-old male with axillary lymphadenopathy. We hope to raise awareness that melanoma of unknown primary can present in lymph nodes without external structural changes.