Chapter 4: Cancer incidence in Canada: trends and projections (1983-2032) – Melanoma - HPCDP: Volume 35, Supplement 1, Spring 2015

Chapter 4: Projections by Cancer Site

9. Melanoma

Cutaneous malignant melanoma (referred to as melanoma) is the eighth most common cancer in Canadian males and the seventh most common in Canadian females.^{Endnote 1} One in 63 males and 1 in 79 females can expect to be diagnosed with melanoma in their lifetime, and 1 in 287 males and 1 in 420 females can expect to die from it.^{Endnote 1} In 2003–2007, the average annual number of new cases of melanoma was 2320 for males and 2055 for females, or 2.9% and 2.8% of all male and female cases, respectively (Tables 4.9.1 and 4.9.2). During 1998–2007, melanoma ASIRs increased significantly in both sexes by 1.4% per year (Figures 3.1 and 3.2). The 5-year relative survival rates for melanoma diagnosed between 2006 and 2008 were 85% for males and 92% for females.^{Endnote 1}

Melanoma is one of the most frequently diagnosed cancers in young adults. The ASIRs in 2003–2007 increased with age to 79.8 per 100 000 in men aged 85 or older and to 37.1 per 100 000 in women of the same age, with the increase being steeper in men than in women for those aged 55 or older (Tables 4.9.3 and 4.9.4).

The rates were up to 1.6 times higher in females than in males in those under age 45, approximately equal in the 45–54 age group, and up to 2.1 times higher in men than in women above 55. The observed differences between sexes increased with time in each age group except in the 45–54 age group (Figure 4.9.2).

From 1983–1987 to 2003–2007, melanoma ASIRs in males increased steadily in all regions, with the most pronounced increase in Atlantic Canada (Figure 4.9.1). The increase was not evident in the Prairies and less steep in Quebec in the last observation period (2003–2007). For females, the ASIRs in the Atlantic region, the Prairies and Quebec increased to their peaks in 1998–2002 and then displayed a downward trend at different levels, while the observed rates in Ontario continued to increase. In contrast, British Columbia rates decreased steadily until 1998–2002 and then turned into an upward trend.

The ASIRs of melanoma in males are projected to peak after 5 years in the Prairies and Quebec, and after 10 years in the Atlantic region, Ontario, British Columbia and Canada as a whole (Figure 4.9.1). The rates for females are predicted to peak after 15 years in Ontario, British Columbia and Canada as a whole, and after 20 years in the Atlantic provinces; whereas the rates in the Prairies and Quebec will continue their most recently observed downward trends. There are regional differences in ASIR levels, but the internal ranking of the regions is similar for males and females. When Quebec is excluded from assessing regional variation because of underreporting in the numbers of cases,Endnote 42, Endnote 43 the lowest incidence rates of melanoma are forecast to be in the Prairies and the most elevated rates, in the Atlantic region and in males only in Ontario.

From 2003–2007 to 2028–2032, melanoma ASIRs in Canada are projected to peak and then decrease by 6% in males, from 13.1 to 12.4 per 100 000, and to increase by 5% in females from 10.7 to 11.2 per 100 000 (Tables 4.9.3 and 4.9.4). The annual number of male cases is projected to rise by 75%, from 2320 to 4065, and the number of female cases is projected to rise by 69%, from 2055 to 3465 (Tables 4.9.1 and 4.9.2).

In Quebec, because of the registry's dependence on hospital data before 2008, the numbers of melanoma cases are believed to be underreported.^{Endnote 130} Allowing for the expected number of Quebec cases after adjustment for underreporting, the annual increase in melanoma incidence for Canada from 2003–2007 to 2028–2032 would be approximately from 2480 to 4295 cases in males and from 2195 to 3640 cases in females. The adjusted annual number of cases in Quebec would increase over this period from approximately 460 to 660 in males and 405 to 490 in females. The corresponding prediction for the adjusted age-standardized rates in Quebec would be a decrease from 10.7 to 9.1 per 100 000 in males and a decrease from 8.8 to 7.6 per 100 000 in females.

Comments

According to IARC, about 80% of melanoma is caused by exposure to ultraviolet (UV) radiation^{Endnote 86} (from the sun and sunbeds). The risks associated with intense and intermittent exposure tend to be greater than those associated with chronic exposure, especially for younger people.^{Endnote 131} A history of sunburn doubles the risk.^{Endnote 132, Endnote 133} People with fair complexions, light eyes, red hair colour, or multiple benign or dysplastic nevi are at higher risk.^{Endnote 52, Endnote 134, Endnote 135, Endnote 136, Endnote 137} The presence of a family history of melanoma doubles the risk of developing the disease.^{Endnote 138, Endnote 139} Around 10% of melanoma cases are attributable to inherited risk.^{Endnote 111, Endnote 140}

Based on an assumption that risk of melanoma will continue to decrease in the more recent birth cohorts (data not shown),^{Endnote 141} our analysis shows that the increase in melanoma incidence rates is projected to slow down appreciably in both sexes, and that rates are expected to decrease after 10 or 15 years. The statistical model demonstrates that in male melanoma in Canada, the last 3 estimated cohort coefficients are negative and the earlier cohort coefficients positive, so moving and applying these cohort values to older age groups could decrease the rates. In terms of risk factor, this is likely due to reduced exposure to carcinogenic ultraviolet rays through primary prevention programs aimed at reducing sun exposure and enhancing public awareness. Data to enable the monitoring of trends in sun exposure and sun behaviour of Canadians are lacking and are urgently needed. The projected downturn of melanoma incidence rates in Canada, especially in British Columbia and Ontario, is also possibly linked to the increasing immigration from rare areas of melanoma (such as Asia).^{Endnote 105, Endnote 106, Endnote 141}