“The most striking results from these analyses relate to increasing incidence trends among younger adults for breast, colorectal, pancreatic, endometrial and kidney cancers,” writes Dr. Darren Brenner, Cumming School of Medicine, University of Calgary, with coauthors. “Obesity is a risk factor for these cancer sites, and the rising incidence runs parallel to the growing prevalence of obesity in recent decades.”
The study, which included almost 5.2 million cancer cases diagnosed in Canada between 1971 and 2015, looked at cancer trends by age and birth cohort (patients grouped by year/decade of birth). Cancer incidence — the rate of new cases — is well documented in Canada, but less is known about trends by age groups.
“The trend among younger adults is of greater concern because they are ineligible for most cancer screening programs,” write the authors.
Other key findings:
- There has been an overall increase in cancers not normally occurring at younger ages, particularly breast and colorectal cancer.
- The highest increase in cancer incidence is for women aged 30-39 years.
- Cancer incidence has decreased in women aged 80-89 years.
- The most recent trends show statistically significant decreases in the incidence of cervical, lung, bladder and prostate cancer, across most age categories.
- The overall recent decrease in cancer incidence is due to declines in cancer in people older than 50 years.
The reductions in cancer incidence across age groups for several cancer types are most likely the result of primary and secondary prevention activities, including smoking cessation programs, which have decreased lung cancer, and sun safety behaviours, which have led to lower rates of melanoma in women younger than 40 and in men younger than 50 years. Endoscopy and fecal-based screening programs for colorectal cancer and screening for cervical cancer have contributed to declining rates in these cancers.
However, a rise in the use of prostate-specific antigen (PSA) testing resulted in sharp increases in prostate cancer diagnoses between 1990 and 2007, and thyroid cancer has also been over-diagnosed.
Age-specific cancer rates over time help identify the impact of changes in practice such as screening programs, better diagnosis and changing risk factors. Further efforts to reduce obesity, promote additional cancer prevention programs and further research into risk factors that may be causing cancer in younger age groups are essential.