Metastatic melanomas of unknown primary show better prognosis than those of known primary: a systematic review and meta-analysis of observational studies.

Background: Melanoma of unknown primary (MUP) is a condition of metastatic melanoma without a primary lesion.

Objective: We sought to identify the prognosis of MUP compared with melanoma of known primary (MKP).

Methods: We searched for observational studies containing at least 10 patients with MUP from MEDLINE and EMBASE from inception to December 22, 2012. The outcomes of interest were overall and disease-free survival; meta-analyses of hazard ratio stratified by stage using a random effects model were performed. In addition, second systematic review identified risk factors influencing the survival of patients with MUP.

Results: Eighteen studies including 2084 patients with MUP and 5894 with MKP were included. MUP had a better overall survival compared with MKP in stage III (15 studies; hazard ratio 0.83, 95% confidence interval 0.73-0.96, P = .010) and stage IV (6 studies; hazard ratio 0.85, 95% confidence interval 0.75-0.96, P = .008). Secondly, 22 studies including 3312 patients with MUP were reviewed, and increased stage and old age were the risk factors in patients with MUP.

Limitations: Diverse observational studies were reviewed, and selection and reporting biases are possible.

Conclusions: The current meta-analyses suggest better survival outcomes in patients with MUP than those in patients with MKP with the same corresponding tumor stage.