The overall rate of new cancer cases is decreasing in men but increasing in women younger than 80 years, and obesity-related cancers are increasing in young people, according to a study on cancer trends in Canada from 1971 to 2015. The findings, ‘Age-standardized cancer-incidence trends in Canada, 1971–2015’, published in Canadian Medical Association Journal, 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 is well documented in Canada, but less is known about trends by age groups.
"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 co-authors. "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 trend among younger adults is of greater concern because they are ineligible for most cancer screening programs," write the authors.
The key finds were:
- 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 programmes, 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 faecal-based screening programmes 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.
“Overall, we found large reductions in cancer incidence across age groups for several cancer sites that are probably attributable to efforts in primary and secondary prevention. The overall increase in early-onset cancers, particularly breast and colorectal, highlights the importance of efforts to reduce obesity rates as a measure for cancer prevention,” the authors concluded. “...Future studies should examine similar age-specific incidence trends by province, which may allow the identification of relevant etiologic factors and prevention efforts that are contributing to recent changes.”
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