The prevalence of non-melanoma and squamous skin cell cancers have risen by 30 per cent in Ontario over the past two decades, according to a new analysis that pins part of the blame on the popularity of artificial tanning booths.
The findings, published in the Canadian Medical Association Journal, are the result of efforts by researchers to better understand and raise awareness of the risks presented by keratinocyte carcinomas, the most commonly diagnosed malignancies in the country. Researchers analyzed data from the Institute for Clinical Evaluative Sciences — a community of research, data and clinical experts — from 1998 to 2017 and found that after a small decline in prevalence during the first five years of study, rates reversed course and became a troubling trend.
Non-melanoma skin cancer accounts for around 28 per cent of all new cancer cases in the country, according to the Public Health Agency of Canada. Around 75 to 80 per cent of these cases originate in the basal cells lining the top layer of the skin and are known as basal cell cancer (BCC). The remaining 20 to 25 per cent form in the squamous cells and are known as squamous cell cancer, or SCC. Because non-melanoma cancers are often successfully treated by dermatologists and do not require hospitalization, other statistics surrounding the disease are often estimates. It is thought that one in eight Canadians will develop BCC in their lifetime and one in 20 will experience SCC. Both forms of the disease have a higher five-year survival rate than melanoma, a less common but deadlier form of skin cancer.
Researchers in the current study found the annual rate of mortality from keratinocyte carcinomas — a term encompassing non-melanoma and squamous skin cell cancers — rose almost five-fold over the period of observation, from 6.39 deaths per 100,000 in 1998 to 30.53 deaths in 2017. The rate of death was roughly 1.8 times higher in males than females and most deaths occurred after the age of 65.
The team speculated that skin cancer prevention campaigns in the decades prior to the period of study may have accounted for the early decrease in prevalence — a trend they suspect was countered by the rising popularity of tanning booths and other behaviours. Dividing the data into age groups revealed that females between 45 and 64 experienced a greater prevalence of these cancers than males of the same age and that the annual incidence of new cases was greatest before the age of 35.
“Our findings highlight the importance of stratifying by age when evaluating differences by sex in a population,” said An-Wen Chan, a co-author of the study and professor at Women’s College Hospital and the University of Toronto. “Evidence suggests that males are more likely to have outdoor occupations and are less likely to engage in sun protective behaviours and females are more likely to seek a tan through artificial tanning booths and sun exposure.”
Researchers pointed out that while the tendency to suntan among young females declines with age, this group is also more likely to examine their skin closely, a behaviour that may increase the likelihood of diagnosis. Any way the data is divided, however, the rates of skin cancer are clearly trending in the wrong direction.
“The increasing incidence rates (particularly in younger females) and disproportionately rising mortality rates of keratinocyte carcinoma are concerning,” the analysis concluded. “Further research is necessary to evaluate the reasons for the epidemiological trends. Renewed public health efforts are warranted to promote preventive measures, patient education and early diagnosis.”
Dave Yasvinski is a writer with Healthing.ca