A UK study has suggested that men at a high genetic risk for bowel cancer can benefit from healthy lifestyle changes, according to a risk model that looks at both genetic and non-genetic factors. The exact reliability of the figures is tricky to determine due to the assumptions that had to be made, but the underlying finding that such a model can be used to help target screening and prevention still seems sound.
In Brief: Bowel Cancer
Colorectal (bowel) cancer is a recurrent public health issue in developed countries. Presently, the five year survival rate for patients is only 55%, which leaves very large room for improvement. Early detection and prevention is thought as one way to help improve patient outcomes, so finding a way to know which people such measures would help most is important.
Bowel cancer has a strong heritable element and some known modifiable (lifestyle) risk factors as well. The study is an attempt to use predictive modeling to develop a comprehensive risk score for bowel cancer and to see who would be able to benefit most from screening and prevention techniques.
The model included all 37 known genetic risk features for bowel cancer as well as the modifiable ones: body mass index, alcohol, red meat, fruits, vegetables, smoking, level of physical activity, aspirin use, and inflammatory bowel disease. Levels of absolute risk were derived from UK population and incidence/mortality data. Following some number crunching, the following findings were made:
- 42.2% of men aged 55-59 with colorectal cancer had a risk at least as high as the average 60 year old (60 is minimum eligible age for UK screening)
- For every 10,000 50-year old man with the highest level of risk factors, 760 cases of bowel cancer could be prevented over a 25 year period via modifiable risk factors
- However, in those with the lowest level of risk, only 90 could be prevented for every 10,000 people
The ultimate conclusion was that colorectal cancer screening and prevention based on modifiable risk factors could have the best effects if targeted at those with the highest risk, according to the model.
The researchers admit to certain weaknesses in their model that could affect the reliability of the results. These include:
- The model relied on the assumption that genetic and lifestyle risk factors had a multiplicative effect on bowel cancer risk
- The impact of chemo prevention and lifestyle changes on risk was assumed to be uniform across things like race or physical characteristics
- The assumptions of how independent lifestyle factors were from each other in terms of risk influence may be inflated if it is found their population estimates were off
The study suggests that bowel cancer screening on the highest risk men, and the promotion of healthy lifestyle changes, could have the most benefit for preventing bowel cancer. Calculating the exact strength of this benefit required certain levels of assumptions that may influence how things work out in the real world.
Frampton, M., et. al., “Modeling the prevention of colorectal cancer form the combined impact of host and behavioral risk factors,” Genetics in Medicine, 2016; 10.1038/gim.2016.101.