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

Abstract

Melanoma of unknown primary (MUP) is a condition of metastatic melanoma without a primary lesion. We sought to identify the prognosis of MUP compared with melanoma of known primary (MKP). 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. 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. Diverse observational studies were reviewed, and selection and reporting biases are possible. The current meta-analyses suggest better survival outcomes in patients with MUP than those in patients with MKP with the same corresponding tumor stage.