TORONTO — A study by Toronto researchers says the prevalence of non-melanoma skin cancer is on the rise in Ontario, climbing by 30 per cent from 2003 to 2017 following a period of decline decades earlier.
Scientists from the University of Toronto and Women's College Hospital analyzed data from the Institute for Clinical Evaluative Sciences (ICES) on skin cancers known as keratinocyte carcinomas over a 20-year period.
They involved cancers that formed in cells of either the lower or upper layers of the skin, as opposed to the melanin-producing cells deeper in the epidermis, which tend to be more serious.
In 2017, the incidence rate reached 369 per 100,000 males and 345 per 100,000 females.
Authors of the study said non-melanoma skin cancers are the most common malignancies in Canada and "can cause substantial illness and affect quality of life" despite a low mortality rate. But the study also suggests annual mortality rates for skin cancer are climbing, rising almost five-fold to 30.53 deaths per 100,000 in 2017, up from 6.39 deaths per 100,000 in 1998.
While most deaths occurred in adults older than age 65, the study found the annual incidence rate of new cases was highest in people younger than 35.
Dr. An-Wen Chan, one of the study's co-authors and a dermatologist and skin cancer surgeon at Women's College Hospital, said he had noticed clinically that rates of the disease seemed to be increasing, leading his team to formally examine data across the province.
"When we looked deeper into the data and categorized patients by age and by sex, very clear patterns emerged, which were surprising to some degree," Chan said. "We found that younger people have the most rapidly increasing rates of skin cancer, particularly younger women.
"We were also surprised by how quickly death rates seem to be increasing over the 20-year period — an average of eight to nine per cent increase per year."
The study, published Monday in the Canadian Medical Association Journal, found the incidence rate was higher in women younger than 55 and in men aged 55 or older. It also found rates of non-melanoma skin cancers were rising more quickly among women aged 45 to 64 years than in men of the same age range.
The data from ICES included adults aged 18 and older living in Ontario from January 1998 through December 2017. Researchers excluded patients who had previous keratinocyte carcinoma diagnoses, analyzing only new instances of the disease.
Rates of non-melanoma skin cancer had decreased in the early part of the study period from 1998 to 2003 before reversing over the remaining 14 years.
The study suggests the early period of decline may be due to skin cancer prevention campaigns in the 1980s and 1990s, while later increases could be linked to the popularity of artificial tanning booths and other behaviours.
Exposure to tanning is highest in young females and declines with age, Chan said, but women are also more likely than men to examine their skin, which could lead to earlier diagnosis.
The Canadian Skin Cancer Foundation says non-melanoma cancers can present as persistent, non-healing sores, reddish patches, shiny bumps or wart-like growths that can occasionally bleed, depending on the type.
Chan said the increasing incidence rates and rising mortality rates of non-melanoma skin cancers are concerning.
While the study period ended in 2017, Chan said the pattern likely "would not have changed" in the four years since then. Incidence and mortality rates could keep increasing if the COVID-19 pandemic hinders early detection and treatment for some people, he added.
"We are seeing patients with larger, more advanced tumours presenting for treatment at a later stage," he said.
The study said more research and renewed public health efforts to promote preventive behaviours and encourage early diagnosis are needed.
Chan said governments and stakeholders could consider more educational campaigns around sunscreen and protective clothing and urge people to see a doctor when they have "suspicious skin lesions."
"It's critical to promote early detection," he said. "The more advanced the tumour at the time of diagnosis, the more challenging it is to treat."
This report by The Canadian Press was first published Oct. 4, 2021.
Melissa Couto Zuber, The Canadian Press
