Calculating Preventable Cancer Cases: Understanding the Science Behind Lifestyle Choices
According to a report by the Cancer Registry commissioned by the Norwegian Cancer Society, by eliminating specific risk factors, 13,383 out of 20,702 cancer cases could have been avoided, which represents preventing over one in three of the 35,000 total annual cancer cases in Norway. The report calculated how many cases of cancer in Norway can be attributed to certain risk factors to highlight the potential for cancer prevention through lifestyle changes on a population level. Among the major risk factors for cancer are smoking, UV exposure, diet, obesity, and alcohol. The report's findings are based on a theoretical scenario that assumes the complete elimination of these risk factors.
Dr Trude Eid Robsahm, the report's lead author, is heading the section for Etiology, within the Cancer Registry´s Research Department. She has a particular interest in the role of modifiable lifestyle factors in primary and secondary cancer prevention.
Lauri Beekmann, NordAN: Can you explain, in simple terms, how you calculated the cancer cases that could be preventable?
Dr Trude Eid Robsahm: First, we used the literature to select modifiable risk factors that are associated with cancer risk with strong evidence. We only included cancer forms that were associated with each of the risk factors, with strong/probable evidence. So cancer forms with weaker associations were not included.
The estimation is based on three factors;
a) The incidence of related cancer(s) in the Norwegian population (averaged over a 5-year time period 2016-2020, to avoid annual variations)
b) The prevalence of each of the risk factors in the Norwegian population (for age groups 0-50 and 51-85 years, obtained from national registries or population-based health surveys for a time period that was on average 10 years prior to the cancer period (around 2010).
c) Established estimates for the relationships between each risk factors and given cancer (for the risk category), which were obtained from meta-analyses and review publications.
So, based on a-c, we were able to estimate the number of cancer cases for each of the related cancer forms that could be attributed to each of the risk factors in a situation of no exposure for each of the factors (an unrealistic scenario, though).
The report highlights the role of unhealthy lifestyles, including alcohol consumption, in causing cancer. How significant is alcohol consumption compared to other risk factors like smoking and UV exposure?
In total, alcohol intake was not among the risk factors that caused the highest number of cancer cases, but there might be some underestimation here. The prevalence of alcohol intake is based on self-reported intake from surveys, which may give some underreporting. However, if looking into the specific cancer forms, we estimated that alcohol consumption accounted for 221 breast cancer cases annually, a similar number as calculated due to factors such as physical inactivity, obesity or menopausal hormone treatment.
Were the results surprising to you? We have read that, at best, 40-50% of cancer cases could be prevented if lifestyle choices were better. Does that mean that we have actually underestimated the role of one's lifestyle?
No, the results did not surprise me, as they were in line with estimates reported from comparable countries. It was more a confirmation of the situation that we have a similar potential for prevention based on our prevalence of the modifiable risk factors and our cancer rates. Our estimates are based on an unrealistic situation (no one is exposed to the risk factors), which may be an overestimation of what we are able to prevent. We only included cancers strongly associated with the exposures in focus, which is quite conservative, and there might be more cases that could be prevented if being less conservative. However, our results emphasize the need for more knowledge about the effect of lifestyle choices on a population level and emphasize the urgent need for better facilitation on the community level to give people a real choice by making it easier to choose healthy.
These main risk factors point to people's voluntary choices. These are not something like air quality or work environment, where a person can´t change much. Is that good or bad news? Because we are not very keen on changing our life choices.
This is a good thing. The challenge is, however, to make people choose less exposure (healthier lifestyle). But, as I said above, people need knowledge to understand the risk, although information is not necessarily enough. It is a social responsibility to facilitate a healthy lifestyle (through regulation and policies). Price matters a lot for our choices, e.g. as long as healthy food is the most expensive, people cannot necessarily choose. In addition, we need to be nudged towards more healthy choices. Legislation of tobacco in Norway (price, risk communication and banning of marketing and use in all public areas) has significantly decreased the smoking population and prevent the youngest from starting. These measures have changed our attitude to smoking, which is preventive by itself.
In your view, what should be done to get this message out to people concerning their lifestyles? And what is the role of regulation and policies?
Numbers are impactful. People should know about numbers, e.g. alcohol consumption (also low intake) and insufficient physical activity cause more than 200 breast cancer cases each, annually. We (researchers and professionals) are obliged to let people and politicians know. In terms of dissemination, we have a job to do. We need to be more creative, structured and to spend more resources to hit broadly and targeted. Also, we must act agreed and keep up a high intensity for prevention measures. For several of these factors, e.g. alcohol consumption, structural measures are necessary to succeed (as exemplified for smoking, as price and availability), and a change of attitude (more attractive to be associated with no-intake). Influencers are strong voices, can they be used? We may need to understand their acting mechanisms and use their tools.