Improved Survival for Stage IV Melanoma From an Unknown Primary Site

Abstract

We previously demonstrated a survival advantage for nodal metastasis of melanoma from an unknown primary (MUP) versus melanoma from a known primary (MKP). We hypothesized that this survival benefit would extend to MUP patients with distant (stage IV) metastasis. We reviewed prospectively acquired data for 2,247 patients diagnosed with American Joint Committee on Cancer stage IV melanoma at our cancer center between 1971 and 2005. Cox regression analysis in a multivariate model identified prognostic factors significant for survival. MUP and MKP patients were then matched by significant covariates. Overall survival (OS) was estimated by Kaplan-Meier method and compared by log-rank analysis. There were 1,849 MKP and 398 MUP patients. Multivariate analysis of patients with complete data sets identified known/unknown primary (hazard ratio [HR], 1.141; P = .032) and five other significant covariates: age (HR, 1.148; P = .007), sex (HR, 1.17; P = .001), site of metastasis (HR, 1.336; P < .001), number of different metastatic sites (HR, 1.303; P < .001), and decade of diagnosis (HR, 0.713; P < .001). Prognostic matching yielded 392 MUP-MKP pairs. Median OS and 5-year OS rate were significantly greater (P < .001) for MUP patients than for all matched MKP patients or for MKP patients matched by M1 category (for M1b and M1c) or number of metastatic sites. The survival advantage previously reported for patients with stage III MUP also applies to patients with stage IV MUP. The mechanism responsible for this improved survival may provide clues for more effective treatment of stage IV melanoma and therefore warrants further investigation. The improved results for MUP suggest that these patients deserve aggressive therapy.