Background:The aim was to determine whether the increasing age-standardized incidence of malignant melanoma of the skin in some countries can be explained by a suddenly imposed environmental stress to the whole population.Material/Methods:Incidence data were retrieved from the cancer registries of the USA and four Nordic countries. A four-parameter incidence model was developed and its parameters were varied to optimally fit age-standardized data from the investigated countries. Two parameters were used for a log-normally distributed exposure time to illness; the other two were the starting year for the imposed exposure and the critical age (age at which the exposure starts having an effect on incidence). Reported age-specific incidence data from the investigated countries were also analyzed to see at what age melanoma of the skin actually starts to occur.Results:Similar parameters for exposure time to illness were calculated for all five countries. The staring year was found to be 1967 for the USA, while for the Nordic countries it ranged between 1953 to 1955. The modeled critical age for all countries varied from 13 to 18 years; the actual average critical age was found to be 14.3 years for the investigated countries analyzed based on reported age-specific data.Conclusions:An environmental stress suddenly imposed in the mid-1950s for the Nordic countries and in the late 1960s for the USA, affecting people from 13 years of age and above, can mathematically explain the age-specific pattern for melanoma of the skin noticed in the investigated countries.

Keywords: Age Distribution, Environmental Exposure, Incidence, Melanoma - etiology, Registries, Scandinavia - epidemiology, Skin Neoplasms - etiology, Sunlight, United States - epidemiology