Rise in Keratinocyte Carcinomas Cause for Concern

Basal and squamous cell cancers, known as keratinocyte carcinomas, carry a low mortality rate but are the most common malignancies in Canada. Between 2003 and 2017 in Ontario, the rate of these types of skin cancers increased by 30%, according to new research in Canadian Medical Association Journal.

Despite its low mortality rate, keratinocyte carcinoma negatively affects patient quality of life and morbidity, and adds to health care costs. Conducting epidemiological studies on this type of cancer is also a challenge because it is excluded from most cancer registries in North America, the study authors noted. In the current population-based retrospective study, they aimed to evaluate incidence and mortality rates of keratinocyte carcinoma and describe differences based on sex.

Using linked health administrative databases, they identified keratinocyte carcinoma through health insurance claims with a validated algorithm, from 1998 through 2017. Deaths related to keratinocyte carcinoma were identified from death certificates. The researchers used the average annual percentage change (AAPC) based on joinpoint regression to evaluate trends in incidence and mortality stratified by sex, age group, and income.

Adults aged 18 or older who were eligible for health coverage under the Ontario Health Insurance Plan (OHIP) were included in the population. The annual incidence rates were calculated based on first diagnosis as determined by the algorithm, which uses data from reimbursement claims within a 180-day period in the OHIP claims database.

There was a notable pattern in annual instances, with rates declining annually from 1998 to 2003 (328.6 and 274.2 per 100,000 adults, respectively). But from 2004 to 2017, there was a steady increase in incidence, and by 2017, the rate was 356.7 per 100,000. This was a 30% change over 14 years, or an AAPC of 1.9% (95% CI, 1.7%-2.1%).

Similar trends were seen between men and women, but age played a larger role in annual instances of keratinocyte carcinoma. In 2017, the rates were 369 per 100,000 men and 345 per 100,000 women but were higher in men aged 55 and older and lower in women aged 55 and younger. Older age is also a well-established risk factor in skin cancer, given the older population’s greater cumulative sun exposure over time. The incidence rate was also higher in men in higher-income quintiles.

Overall, the annual mortality rate was a median of 1.8 times higher in men than in women. Since metastasis is very rare for basal cell carcinoma, deaths can mostly be attributed to squamous cell carcinoma.

In adults aged 65 years and older, the annual mortality rate increased to an AAPC of 7.7% (95% CI, 4.7%-10.8%) in women and 8.9% (95% CI, 6.1%-11.7%) in men compared with 4.7% (95% CI, 2.9%-6.6%) in younger adults as a whole.

“Our findings highlight the importance of stratifying by age when evaluating differences by sex in a population,” the authors wrote. Income quintiles did not display any consistent mortality rate differences.

The study also showed that rates of keratinocyte carcinoma were much higher than those reported in other Canadian provinces, which the researchers attribute to the validated algorithm used in the current study. As to the rise in cases following 2003, they note that the use of artificial tanning booths and decline of sun protection measures may have played a part.

“Further research is necessary to evaluate the reasons for the epidemiological trends,” the authors concluded. “Renewed public health efforts are warranted to promote preventive measures, patient education, and early diagnosis.”

Reference

Tang E, Fung K, Chan A. Incidence and mortality rates of keratinocyte carcinoma from 1998–2017: a population-based study of sex differences in Ontario, Canada. CMAJ. 2021;193(99):E1516-E1524. doi:10.1503/cmaj.210595