Gut bacteria linked to bowel cancer?
There has been a lot of focus on the 'microbiome' recently – the collection of literally trillions of microbes in the gut – and their potential connection to a range of conditions affecting the gastrointestinal system. A few recent studies have attempted to shed some light on whether there is any causative link between the makeup of the microbiome and disease.
A research team at the Federal University of Viçosa in Brazil(1) has undertaken a review of a range of studies looking at this very issue, and has found a possible connection between particular microorganisms in the gut and bowel (colorectal) cancer.
The research team came to three conclusions…
- Inflammation – some bacteria capable of stimulating inflammation in the gut may also cause or assist in the development of bowel cancer, and so people with inflammation affecting the intestine may be more prone to developing bowel cancer
- Toxin-producing bacteria – some bacteria, for example E. Coli, excrete toxic molecules that can affect the behaviour of cells in the lining of the gut, including cell division and so may prompt uncontrolled cell division – the major hallmark of cancer. Other bacteria known to excrete carcinogenic substances include B. Fragilis and Clostridium, which can in turn encourage cancer to develop and/or cause benign tumours to become cancerous
- Presence of a particular strain called Fusobacterium increases the risk of developing (benign) adenoma by a factor of 3.5
Interestingly, the same research team acknowledged the positive impact of some microbes – specifically those that excrete butyric acid – in terms of having a protective effect and reducing the risk of developing bowel cancer. They advised that consumption of foods such as some types of cheeses, pickles and yoghurt would encourage these protective 'probiotic' microbes.
Are current cancer statistics misleading?
A very recently published study(2) suggests that some current cancer risk statistics may be misleading. Current statistics for lifetime risk of contracting common Australian cancer types (breast, bowel, melanoma, lung, prostate) are based on the 'co-morbidity model' used by the Australian Institute of Health and Welfare (AIHW) from 1982-2013. A different risk calculation model called 'competing mortality' results in lower risk factors, as it takes into account that if a person dies from another cause – a 'competing risk' – they cannot continue to be considered at risk of contracting other diseases after they have died. Although this is a fine point, the fact that the competing mortality model is now in use in the UK and North America means that statistics from Australia cannot be directly compared with the UK/US and this would cause some confusion.
Examples of the differences show small, but significant decreases, for example the lifetime risk of contracting colorectal cancer for men is 7% when applying the competing mortality approach, as against a 9% risk using the co-morbidity model.
Research co-author Paul Glasziou explained…
“It’s not that the figures have been hugely inaccurate, but people quote them – so we think they need to be corrected to appropriately take into account the competing risks. Across the board, most statements about the lifetime risk of cancer have been overestimated because competing risks aren’t taken into account. If you die of a heart attack at 65, you can’t die of cancer at 75 – but the current research acts as if you could.”
Bowel cancer screening to get easier
This month the National Bowel Cancer Screening Program (NBCSP) merged with the National Cancer Screening Register. The former was responsible for the distribution of iFOBT tests to people aged 50-74. With the merger of the two bodies, the National Register will support this program by reminding people eligible for the free test and by improving support and follow up for people receiving positive tests.
From next year the NBCSP will offer all eligible Australians aged 50-74 bowel cancer screening every two years, thus potentially significantly reducing the burden of bowel cancer and saving 500 lives annually.
- Intestinal microbiota and colorectal cancer: changes in the intestinal microenvironment and their relation to the disease Journal of Medical Microbiology Oct 2019 https://www.microbiologyresearch.org/content/journal/jmm/10.1099/jmm.0.001049
- Is the risk of cancer in Australia overstated? The importance of competing mortality for estimating lifetime risk Nov 2019 Medical Journal of Australia https://onlinelibrary.wiley.com/doi/abs/10.5694/mja2.50376