Cancer Now Accounts for 1 in 3 Deaths; Prevention Is Key

Kristin Jenkins

May 22, 2019

Canadians are continuing to smoke, drink, and eat their way to a diagnosis of cancer — in spite of public health strategies that could prevent up to 40,000 cancer cases per year, according to experts.

Findings from the Canadian Population Attributable Risk of Cancer (ComPARe) study show that in 2015, more than one third of cancers were caused by "largely preventable" lifestyle, environmental, and infectious agent risk factors.

If this trend continues, the annual number of cases of preventable cancer in Canada is projected to almost double, to about 102,000 by 2046.

So says a research team led by Christine M. Friedenreich, PhD, of the Cumming School of Medicine at the University of Calgary, and CancerControl Alberta, Canada.

Cancer is now the leading cause of death in Canada, responsible for 1 in 3 deaths in 2017, the authors state in a special report published online May 6 in Preventive Medicine.

"While it is true that much progress is needed to find better treatments for cancer, studies such as that conducted by the ComPARe consortium show unequivocally that there is much that can be done to prevent cancer," said guest editor Salaheddin M. Mahmud, MD, PhD, Department of Community Health Sciences, University of Manitoba, in a statement.

The study shows that out of 187,070 cases of cancer diagnosed in 2015 among Canadians ages 30 years or older, 33% can be attributed to one or more modifiable risk factors. There were no significant differences between men and women.

The most common preventable cancers were those of the cervix, lung, and head and neck.

Smoking tobacco remains the king of cancer risk factors, responsible for more than 18% of all cancers diagnosed in 2015. However, the results also show that the combination of physical inactivity, a sedentary lifestyle, and excess weight accounted for an additional 12% of cancer cases.

Other leading modifiable cancer risk factors include alcohol consumption and human papillomavirus (HPV) infection.

The researchers estimate that more than 11,000 cancers could be prevented each year if people would stop smoking. Similarly, more than 6000 cancers could be avoided by maintaining a healthy weight.

Abdominal Adiposity: Preventable Cause of Cancer

Of all the findings, one of the most surprising was the fact that excess body weight, particularly abdominal adiposity, is projected to replace physical inactivity as the second leading preventable cause of cancer by 2042, said Eduardo L. Franco, DrPH, PhD (Hon), editor-in-chief of Preventive Medicine and director of the Division of Cancer Epidemiology at McGill University in Montreal.

"We did not expect obesity to come as strong as it did," Franco told Medscape Medical News. "As others have said, 'obesity is the new smoking.' "

Although the public has been educated about the health risks associated with smoking tobacco for decades, the obesity epidemic "snuck up on us," he said.

The analysis confirms that Canadians are getting fatter every year.

It estimates that 7.2% of associated cancers diagnosed in 2015 were due to excess body weight, with 8.9% of them caused by large waist circumference, and 10% due to a high waist-to-hip ratio (>0.9 for men, >0.85 for women).

All it would take to prevent 42,742 cancers by 2042 is for Canadian adults to reduce their body mass index (BMI) by one unit, the researchers say.

Even better, if Canadians could get their BMIs down to 1994 levels, 72,157 cancer cases could be prevented between now and 2042.

"I think it [obesity] will be a tougher battle than that we brought against smoking," warned Franco, adding: "The issues are far more complex."

Obesity will be a tougher battle than smoking — the issues are far more complex. Dr Eduardo Franco

Disconnect Between What We Know and What We Do

There is a "critical gap" in information about the relative importance of the risks that drive cancer incidence in Canada, writes Mahmud in a related editorial. This is interfering with the efforts of policymakers, clinicians and others to reduce the cancer burden in Canada, he explains.

"The time has come to act on the key discoveries from cancer prevention research and turn them into measurable benefits for the population," Mahmud suggests. "The ComPARe study effort should also serve as a methodological and multidisciplinary roadmap for other countries to conduct their own similar assessments."

To identify actionable targets for cancer prevention, experts in epidemiology, biostatistics, cancer prevention, and knowledge translation analyzed data from the national cancer registry to estimate the current and future cancer burden attributable to various exposures.

Population-attributable risks (PAR) and potential impact fractions (PIF) were used to model current attributable cancers. Then, the incidence of avoidable cancers in the future was projected to 2042 using population-based national health survey data from 1983 to 2012.

The researchers investigated well-known lifestyle risks such as smoking tobacco, drinking alcohol, leading a sedentary lifestyle, and being overweight or obese. They also determined the burden of cancer attributable to occupational and environmental exposures such as radon, and particulate matter.

In addition, they looked at the impact on cancer risk of eating red and processed meat, having a diet low in fruits and vegetables, exposure to ultraviolet radiation (UVR), and infections such as human papillomavirus (HPV).

"What we know about the preventable fraction of cancers that are due to specific modifiable risk factors comes from a good knowledge base of epidemiological studies," commented Franco.

"Although they inform policymaking from the analysis of aggregate statistical data, these preventable fractions have an important meaning for the physician who confronts a patient about his or her lifestyle and habits," Franco said. "The physician can use these preventable fractions to convey to his/her patient a sense of the magnitude of risk."

For one, the analysis showed that the majority of Canadians are not eating enough fruits and vegetables. In fact, 80.5% of Canadians ate less than 4 servings of fruit each day and 86.6% admitted they were guilty of the same low vegetable consumption.

The research team, led by Abbey E. Poirier, MSc, of the Department of Cancer Epidemiology and Prevention Research at CancerControl Alberta, determined that in 2015, 0.7% and 0.3% of all incident cancers were attributable to low fruit and vegetable consumption, respectively.

They calculated that eating just one more serving of fruit and vegetables per week could prevent a total of 20,710 and 10,185 colorectal cancer cases, respectively, between 2015 and 2042.

The analysis also demonstrated a small but meaningful burden associated with eating red and processed meat. This lifestyle choice accounted for an estimated 4.5% of associated cancers and 0.7% of all cancers, according to Darren Brenner, PhD, of the Department of Cancer Epidemiology and Prevention Research at CancerControl Alberta, and colleagues.

The researchers determined that a mean decrease of 0.5 servings/week of red meat or processed meat could prevent about 8700 or 16,600 cancer cases, respectively, between 2015 and 2042.

To decrease the growing burden of melanoma in Canada, sunbathing and indoor tanning behaviors need to be reduced by 50%, say Will D. King, PhD, of the Department of Public Health Sciences at Queen's University in Kingston, Ontario, and colleagues.

They estimate that in 2015, 62.3% of melanomas were attributable to ultraviolet radiation (UVR) exposure. In addition, 29.7% were attributable to the combination of sunburn (7.4%), sunbathing (17.8%), and indoor tanning (7%). Cutting the number of these modifiable UVR behaviors in half could avoid an estimated 11,980 melanoma cases by 2042.

Seven infections were responsible for 3.7% of cancers among Canadian adults in 2015 and represent an important target for reducing the cancer burden, says the research team led by Karena D. Volesky, MD, of McGill University in Montreal.

Many of the infection-attributable cancer cases for 2015 were preventable through vaccination (Hepatitis B, HPV), antibiotic therapy (Helicobacter pylori) or a combination of interventions (Hepatitis C), the ComPARe study shows. Other infections included the Epstein-Barr virus, human herpesvirus type 8, and human T-cell lymphotropic virus type 1.

Exposure to occupational carcinogens is often overlooked, point out Paul A. Demers, PhD, director of the Occupational Cancer Research Centre at Cancer Care Ontario in Toronto, and colleagues. Overall, Demers and colleagues estimate that in 2011, between 3.9% and 4.2% of all incident cancers were due to occupational exposures, accounting for up to 21,800 cases.

Up to 21,200 cancers at five cancer sites — mesothelioma, non-melanoma skin cancer, lung, female breast, and urinary bladder — were attributable to occupational exposure to solar radiation, asbestos, diesel engine exhaust, crystalline silica, and night shift work.

"Many people can't personally control what they're exposed to at work, or don't have the freedom to find a different job," writes Demers in a blog.

"They need support from employers and governments," he emphasizes. "We hope that the evidence we gather from research can inform regulations and policies that will ultimately make workplaces safer for everyone."

Alcohol consumption was linked to 1.8% of all cancers diagnosed in Canada in 2015, including 5.2% of alcohol-associated cancers.

"Under the best case scenario, reducing alcohol consumption to 50% of 2003 levels by 2032 could prevent 70,261 cases by 2042," write Brenner and colleagues.

The ComPARe study was funded by the Canadian Cancer Society. Franco reported that he is editor-in-chief of Preventive Medicine, and has relationships with Merck, GlaxoSmithKline, and Roche. Friedenreich, Mahmud, Poirier, Brenner, Demers, King, and Volesky have reported no relevant financial relationships.

Prevent Med. Published online May 6, 2019. Full text, Editorial

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