Melanoma of unknown primary: New perspectives for an old story

Melanoma of unknown primary site (MUP) comprises 3-4 % of all melanomas. It mostly presents in lymph nodes (LNs), followed by subcutaneous sites, and visceral organs; nevertheless, there is a trend of increase in the relative incidence of visceral counterpart in recent years. Spontaneous regression of the primary lesion is a well-established theory, based on the evidence that melanoma can undergo regression at the primary site. MUP and stage-matched melanoma of known primary site (MKP) share similar prognostic factors. The survival rate of patients with MUP has been compared to those with stage-matched MKP. Multiple studies conducted before the era of novel therapy with immune checkpoint or…