Melanoma of unknown primary is correctly classified by the AJCC melanoma classification from 2009.

Few studies have focused on the prognosis of melanoma of unknown primary (MUP). This study aimed (i) to determine prognostic factors for patients with MUP and (ii) to investigate whether the American Joint Committee on Cancer (AJCC) 2009 classification is suitable for MUP. Among 8897 patients with melanoma attending the university department of dermatology, Tuebingen, Germany, 172 (1.9%) patients with MUP were recorded. Prognostic factors were studied using Kaplan-Meier and multivariate Cox proportional hazard models. Cutaneous and subcutaneous metastases were categorized as satellite/in-transit metastases, lymph-node metastases as regional lymph-node metastases, and all other metastases as distant metastases. Multivariate analysis found AJCC-stage at diagnosis, lactate dehydrogenase at diagnosis, number of metastases and age to be independent prognostic factors for MUP. Multivariate analyses stratified by AJCC stage showed that size of satellite/in-transit metastases (P=0.034) and number of regional lymph-node metastases (P=0.006) were significant for stage III, whereas for stage IV age (P=0.006) and lactate dehydrogenase-level at primary diagnosis (P=0.003) proved to be prognostically important. Patients with MUP can be classified according to AJCC, which presented as the strongest prognostic factor. From a management perspective it is important to notice that the majority of MUP were classified as stage III.