Stage IV melanoma of unknown primary: A population-based study in the United States from 1973 to 2014

Abstract

Background: Melanoma of unknown primary (MUP) is incompletely described on a population level.

Objective: We sought to characterize stage IV MUP in a population-based cancer registry.

Methods: We developed a novel search algorithm to identify cases of stage IV MUP in the Surveillance, Epidemiology, and End Results 18 registries from 1973 to 2014. Cases of stage IV melanoma of known primary (MKP) served as a comparison group. Age-standardized incidence rates, demographic characteristics, adjusted disease-specific survival, and Cox proportional hazard models were calculated for MUP and MKP.

Results: A total of 322 stage IV MUP cases and 12,796 stage IV MKP cases were identified in Surveillance, Epidemiology, and End Results 18 registries from 1973 to 2014. The incidence of stage IV MUP is increasing, particularly for patients younger than 30 years of age. In multivariate analyses, age older than 50 and a lack of surgical treatment were negative prognostic factors for stage IV MUP. Relative survival, but not 5-year adjusted disease-specific survival, was higher for stage IV MUP than for MKP.

Limitations: Limitations include the retrospective study design and possible misclassification of MUP.

Conclusions: The incidence of stage IV MUP is increasing, and stage IV MUP shares similar prognostic factors with stage IV MKP, including age and surgical treatment.

Keywords: Surveillance, Epidemiology, and End Results 18; melanoma of unknown primary.

Conflict of interest statement

Conflicts of Interest: The authors report no conflicts of interest relevant to this work.

Copyright © 2018 American Academy of Dermatology, Inc. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Flowchart of stage IV MUP case selection.

Figure 2

Survival of stage IV MUP and MKP. A) Relative survival and 95% CI for stage IV MUP and MKP. B) 5-year DSS Kaplan-Meier curves for stage IV MUP and MKP adjusted for year of diagnosis, age, sex, race, and surgical treatment.