18 June 2018
June has been designated Bowel Cancer Awareness Month by Bowel Cancer Australia, which aims to ‘raise awareness’ of this disease – officially titled colorectal cancer – as the second leading cause of cancer death in Australia.
I have no doubt whatsoever that the individuals involved in Bowel Cancer Australia are well-motivated people who sincerely desire to help others by promoting the uptake of bowel cancer screening. However, I have several concerns about their messaging and their mission, as I do about all organisations which embrace ‘awareness raising’ as their raison d’être.
My biggest gripes are
- They perpetuate the misunderstanding that detection of early-stage cancer equates to preventing cancer:
If a screening test detects a cancer, then by definition, it hasn’t prevented that cancer – otherwise there would be nothing to detect! - They promote the notion that bowel cancer screening reduces the overall risk of dying by ‘catching cancer early’:
It’s certainly true that various forms of screening reduce the risk of dying of colorectal cancer. The US Preventive Services Task Force, in a comprehensive review of the evidence published in 2016, found that between 17 and 24 deaths from colorectal cancer could be averted for every 1000 people screened, using either faecal occult blood testing (FOBT), faecal immunochemical testing (FIT – the test recommended by Bowel Cancer Australia, and provided for free as part of the National Bowel Cancer Screening Program), flexible sigmoidoscopy, colonoscopy or CT colonograpy.
However, reducing the death rate from bowel cancer doesn’t translate to reducing the death rate overall; as the USPSTF concluded:
“To date, no method of screening for colorectal cancer has been shown to reduce all-cause mortality in any age group.”
Whaaaaat? How can something that reduces the risk of dying of bowel cancer not result in you living any longer? The USPSTF did not offer an explanation, but there are several possibilities:
- Screening itself carries risks. For example, for every 10 000 screening colonoscopies performed, 4 will result in perforation of the colon and 8 in a major intestinal bleeding episode, both of which are potentially fatal. The risk is higher if colonoscopy is performed as part of a diagnostic work-up after a positive finding on a screening test of a different method, such as FOBT or FIT. For example, diagnostic colonoscopies performed after a flexible sigmoidoscopy found evidence of cancer, resulted in about 14 colonic perforations and 24 major bleeding episodes for every 10 000 persons.
- Treatment of colorectal cancer can itself cause death, for example due to the toxicity of chemotherapy drugs, especially in elderly people.
- People often mistakenly think of screening as a cancer preventive strategy, or they may derive a false sense of security when they get the ‘all clear’ on a cancer screening test. In either case, they may become more complacent and less likely to engage in health-promoting behaviour, thus increasing their risk of developing cancer or other chronic degenerative diseases in future. For example, in the NORCCAP trial which assessed the value of flexible sigmoidoscopy screening for colorectal cancer,
“Three years after screening, attenders were more likely to gain weight and were less likely to stop smoking, engage in physical activity and eat fruit and vegetables compared to a randomly chosen sample from the control group.”
- Many of the risk factors for colorectal cancer – obesity, high intake of red meat, sedentary lifestyle – are similar to the risk factors for a host of other chronic degenerative conditions, such as cardiovascular disease. If the bowel cancer that would have killed you at age 75 is detected early and successfully treated, you might still die at 75 of a heart attack if you continue the diet and lifestyle habits that fed the growth of your cancer.
I don’t know about you, but if someone tells me that I should do something because it will ‘save my life’, I expect to actually live longer as a consequence of doing it. Sure, avoiding a grisly death from metastatic bowel cancer is a worthwhile aim, but if I avoid dying of bowel cancer only to die of a stroke, heart attack, or another type of cancer, I’m still going to be dead. My life has not been ‘saved’; I’ve just traded one cause of premature death for another.
True preventive strategies don’t just reduce the risk of dying from one particular disease, as bowel cancer screening does, but improve overall health and as a consequence, decrease all-cause mortality (the risk of dying from any cause) and, most importantly, increase health span (the number of years we can live in good health).
So how do we prevent bowel cancer from developing in the first place? Multiple epidemiological (population-based) studies point the way.
Maintaining a healthy body weight is a good place to start. Roughly 11% of colorectal cancer cases have been attributed to overweight and obesity in Europe, with epidemiological data suggesting that obesity is associated with a 30-70% increased risk of colon cancer in men.
Visceral fat (the kind that wraps around and infiltrates your abdominal organs, as opposed to the subcutaneous fat just under your skin) is particularly hazardous. A systematic review published in 2017, which analysed data from 19 prospective cohort studies, involving 1,343,560 participants, found that people with the largest waistlines had a 42% higher risk of developing colorectal cancer than those with a healthy girth.
Your risk of getting cancer of the butt is reduced by getting off your butt. In people who racked up at least 60 minutes of daily physical activity during their leisure time (i.e. outside of work) were found to have a nearly 40% lower risk of developing colorectal cancer than those who were physically active for 10 minutes or less per day.
The other major modifiable risk factor for colorectal cancer is what you send down the pipe each day. The World Cancer Research Fund International Continuous Update Project published a systematic review and meta-analysis of prospective studies of the relationship between intake of foods and beverages and the risk of developing colorectal cancer. Here’s what they found:
- For every 100 g of red and processed meat that you eat per day, you’ll raise your risk of colorectal cancer by 12%.
- Every 10 g per day increase of ethanol intake in alcoholic drinks bumps up your risk by 7%.
- Every 90g per day increase of whole grains (and yes, that includes gluten-containing grains, which no one needs to avoid unless they have an allergy or intolerance) decreases your risk by 17%.
The average weight of a medium-sized steak sold in Australia is just shy of 200 g. Wash down one of these with a middy of beer each day, and you’ve just jacked up your risk of colorectal cancer by over 30%. Bon appétit.
On the other hand, among North American Seventh Day Adventists (SDAs), those who follow meat-free diets have an almost one fifth lower risk of colorectal cancer than those who eat meat – even though SDAs live a generally healthy lifestyle, with very low rates of smoking and alcohol consumption and higher physical activity levels than the average North American, and those who eat meat tend to eat less of it than non-SDAs.
To its credit, Bowel Cancer Australia is a supporter of Meat Free Week, clearly indicating that those involved in the organisation understand the strength of the link between meat consumption and colorectal cancer. However, the link to Meat Free Week is buried in a crowded footer:
Overall, the prevention message is fleetingly referred to throughout the website (there is only one mention of it on the page dedicated to Bowel Cancer Awareness week) while screening, research, and treatment are emphasised:
Well-meaning organisations such as Bowel Cancer Australia miss crucial opportunities to genuinely save lives and extend health span by glossing over the importance of preventing cancer by adopting a healthy lifestyle. The European Prospective Investigation Into Cancer and Nutrition-Potsdam (EPIC-Potsdam) study found that adhering to just 4 healthy lifestyle behaviours – never smoking, having a body mass index lower than 30, at least 3.5 hours per week of physical activity, and eating a healthy diet (high intake of fruits, vegetables, and whole-grain bread and low meat consumption) reduced the risk of developing a chronic disease by a whopping 78%!
Diabetes risk was reduced by 93%, heart attack by 81%, stroke by 50% and cancer by 36%, compared to participants without any of these healthy factors.
Likewise, the EPIC-Norfolk study, a prospective population study of over 20 000 UK men and women aged 45-79 who had no known cardiovascular disease or cancer at baseline survey in 1993-1997, and who were followed up to 2006, found that those who practised 4 healthy lifestyle behaviours – not smoking, being physically active, avoiding excessive alcohol, and consuming at least five servings of fruit and vegetables per day – had a four-fold lower risk of dying than those who didn’t practise any of these healthy behaviours.
“The mortality risk for those with four compared to zero health behaviours was equivalent to being 14 y[ears] younger in chronological age.”
Now that’s what I mean by ‘saving lives’!
Don’t get me wrong – I’m not discouraging people from availing themselves of bowel cancer screening methods such as FIT. There is clear evidence that IT, along with the faecal occult blood test and flexible sigmoidoscopy, do reduce the risk of dying of colorectal cancer.
But screening to detect existing cancer should play a secondary role in both our societal and individual approaches to cancer, with prevention at front and centre. The effects of cancer screening are specific to that form of cancer – you might say that they equate to ‘rearranging the deck chairs on the Titanic‘ – but the effects of preventive behaviours such as healthy diet, regular physical activity and avoiding smoking and excess alcohol consumption are global: they improve health and reduce the risk of virtually all chronic diseases, while extending healthy lifespan and overall longevity.
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