Immigration is the most likely reason for the generational change in melanoma incidence in Queensland, Australia.

Abstract

The recent report of Aitken et al. stated that the age standardized incidence (ASI) of melanoma is decreasing in people under the age of 40 years in the state of Queensland, Australia.1 In contrast, melanoma incidence is increasing in men aged 60 years or more. However, the authors failed to mention that the data were for the entire population not the susceptible population which has greatly changed over their study period. Not all races are at equal risk for melanoma. For example, the incidence of melanoma in Chinese and Indians living in tropical Singapore is 3 per million.2 In contrast, the incidence of melanoma in tropical Queensland is 750 per million for the entire population.3 The Australian population has tremendously changed since 1981 as can be seen by examining data from the Australian Censuses.4 In the Census, the country of birth of the population is recorded but not the race of the respondents. Country of birth has to be used as a surrogate for race. People with a low risk (PLR) for melanoma are defined as those born in Asia, the Pacific Islands, the Middle East, and Sub-Saharan Africa (APIMESSA), and the estimated number of Maoris living in Australia.4 The risk of PLR developing melanoma does not increase after they migrate to Australia.5 The change in the Australian population has been significant. In the 1981 Census, 3.4% of the population was PLR according to country of birth but in the 2016 Census, this had increased to 13.8%. It also has to be taken into account the number of children born in Australia to PLR. Between 1981 and 2014, there were 8,670,368 births registered in Australia and 13.4% had parents who were PLR (range 5.6% in 1981 to 22.4% in 2014). These children are also at low risk for melanoma. In the state of Queensland, the generational change of the racial composition of the population in the last 35 years has also been profound. Data from the Censuses in 1981 and 2016 are set out in Table 1. They concern the cohort aged under 25 years and men aged 55 or more. The total number PLR was calculated by adding the number born in APIMESSA, the estimated number of Maoris and Australian-born children of PLR. This number was subtracted from the total population to give the susceptible population. In the young generation, the susceptible population has increased at an average of 0.5% a year, far less than the increase in the total population. In contrast, the susceptible population in older men has increased at an average of 4% a year, almost the same rate as the increase in the total population. Another factor that would further reduce the number of susceptible people in the young generation is grandchildren of PLR. This number cannot be estimated from the Census data. The data from Queensland show that the most likely reason for the reduction in the incidence of melanoma in the young cohort is immigration. Aitken et al. used a simulation to prove that immigration did not have any effect on melanoma incidence trends in Australia.6 This simulation has been demonstrated to be flawed.7 Instead of using simulations, epidemiologists have to determine the racial composition of each age group then adjust the data because, with regard to skin cancer, race is a more important risk factor than age. Until this is done, data on incidence of melanoma are unreliable and any statements concerning the success of public health campaigns in Australia are suspect.