Background: Metastatic melanoma of unknown primary origin accounts for approximately 2-6% of all melanoma cases. The prognostic significance of this diagnosis is still controversial.
Methods: Of 3258 patients with malignant melanoma recorded during the period 1976-1996, 2.3% had metastases of unknown primary origin. Anatomic distribution, clinical stage, and survival probabilities were evaluated.
Results: Thirty patients were classified as having cutaneous or subcutaneous in-transit metastases, and they showed a 5-year survival rate of 83%. Thirty-seven patients were classified as having lymph node metastasis, and their 5-year survival rate was 50%. Disseminated disease was diagnosed in only 8 patients, who had a median survival of 6 months. Comparison of survival probabilities for patients with in-transit metastases and unknown primary tumors with the probabilities for those with cutaneous primary tumors revealed a significant advantage for the former group. No significant differences were found for patients with lymph node metastasis when those with unknown primary tumors were compared with those who had cutaneous melanomas with regional lymph node metastasis.
Conclusions: The clinical disease course of patients with metastatic melanoma of unknown primary origin is similar to that of patients with primary cutaneous melanoma when the same clinical stages of the disease are compared. Based on the assumption that the majority of regional metastases develop from completely regressed primary cutaneous melanoma, recommendations for initial staging examinations in patients with unknown primary tumors are given in this article.