The Association Between Geographic Location and Incidence of Merkel Cell Carcinoma in Comparison to Melanoma: An International Assessment

Aim: The aim of this article was to provide worldwide, population-based incidence rates for Merkel cell carcinoma (MCC).

Methods: We included 11,576 cases from 20 countries for time trend analyses (1990-2007) and 11,028 cases (2.5 billion person-years) from 21 countries for the period 2003-2007 extracted from Cancer Incidence in Five Continents. We computed age-standardised incidence rates (World Standard population) per million person years and sex ratios of these rates. We estimated annual percentage changes (EAPCs) of the incidence and studied the association between geographic latitude and MCC incidence. We examined the body site distribution of MCC.

Findings: In the majority of populations, the incidence has increased over time (EAPC, men 2.0-21.0%; women 1.6-27.2%). Rate differences between 1995 and 2007 were typically small (men: 0.8-2.2; women: 0.2-1.7). The incidence was relatively stable in some populations (men: U.S. blacks, Japan, Norway, Denmark; women: Denmark, Norway, Sweden). Incidences from 2003 to 2007 were highest in Australia, New Zealand, the United States and Israel among men and in New Zealand, Australia, Ireland and the Netherlands among women. The incidence of MCC and melanoma among white non-Hispanic males in North America was positively associated with living closer to the equator. The proportion of MCC on the head was higher with advanced age. The head was a less likely primary site among blacks as compared with any other ethnicity.

Interpretation: Several countries showed increases in MCC incidence among white non-Hispanics over time. Latitude closer to the equator was associated with the MCC incidence in North American men, but barely in women, possibly due to occupational sunlight exposure patterns.