Malignant melanoma of unknown primary site. To make the long story short. A systematic review of the literature

IntroductionAlthough more than 90% of melanomas have a cutaneous origin, occasionally it is discovered as a secondary deposit without evident primary site. The aim of this study was to systematically review published literature and analyse data on incidence, presentation, therapeutic interventions, survival and prognostic factors.MethodsWe searched MEDLINE, (search terms Melanom*, unknown origin, unknown primary, indolent, occult) and the abstracts from major congresses of the last 4 years and perused the references of the retrieved relevant articles.Results4348 patients with MUP were reported along with 132,643 patients with Melanoma of Known Primary (MKP). The incidence of MUP was 3.2%. The male to female ratio was 2:1 while the age peak was in the 4th and 5th decades. MUP patients harbouring nodal disease had a median overall survival ranging between 24 and 127 months, 5-year survival rate between 28.6% and 75.6% and 10-year survival rate between 18.8% and 62.9%. MUP patients with visceral disease had median survival times between 3 and 16 months, and 5-year survival rates between 5.9% and 18%. Presence of tumour regression in metastatic sites and low nodal burden were associated with favourable outcome. Potentially curative surgical treatment offered survival advantage in comparison to patients with residual metastatic foci. MUP patients who received adjuvant chemotherapy or radiotherapy paradoxically seemed to fare worse compared to patients observed.ConclusionsThis is the first review to bring together the information of 89 years and to analyze all the potential information accumulated. Although a well know entity no consensus is reached in order to describe MUP presentation, management or prognosis.