Melanoma of unknown primary site: a 33-year experience at the Turin Melanoma Centre

Unknown melanoma occurs as metastasis to skin, nodes or viscera, without a detectable cutaneous primary tumour. We reviewed our database of 4881 melanoma patients, diagnosed and followed up prospectively for a 33-year period. We identified 93 cases of metastatic melanoma without evidence of primary; however, five of these patients had a history of a previous excision of a presumed benign lesion without histological examination and were excluded from analyses. At diagnosis, metastases were cutaneous in 35.3% of cases, nodal in 43.2% and visceral in 17% of cases; in 4.5% of patients, both skin and nodes were involved. In all cases, clinical inspection and staging procedures performed at diagnosis of metastatic disease failed to identify a primary melanoma. In 11 cases (11.8%), extensively regressed pigmented lesions (without evidence of melanoma cells at the histological examination) were documented; moreover, we identified in our series five patients with unknown primary affected by vitiligo. The 5-year and 10-year overall survival rates were 49.6 and 41.4%, respectively, with a median of 4.9 years. The 5-year and 10-year time to progression rates were 39.4 and 32.3%, respectively, with a median of 2.3 years. Survival was longer in females and showed significant differences among patients with skin, lymph node or visceral involvement at diagnosis. In melanoma patients, unknown primary represents a not so rare event, with an uncertain origin. We confirmed the relatively good prognosis of unknown primary melanoma patients, a fact that has to be taken into consideration for their management.