When is best to screen for bowel cancer?
The Daily Mail has reported that, “thousands of lives could be saved if the age at which men are screened for bowel cancer is lowered by 10 years.”
This news story is based on a large Austrian study that aimed to determine the correct age to screen men and women for bowel cancer. It found that the number of screening colonoscopies needed to detect one case of bowel cancer (called the number needed to screen or NNS) was significantly lower in men compared to women across all ages. The NNS in men who were 55-59 years old was similar to women 10 years older (75 versus 81.8 colonoscopies respectively). This and other similar findings led the authors to suggest a need to reduce the screening age in men by approximately 10 years.
This robust study provides important information about the difference in prevalence of bowel cancer in men and women of different ages who took part in a national colonoscopy screening programme.
The applicability of the findings from this Austrian study to the UK is limited in some ways. For instance, in Austria, men and women aged 50 are invited to be screened for bowel cancer using a procedure called a colonoscopy where a camera is used to examine the bowel. In the UK, screening does not take place until men and women reach age 60, at which point screening is performed using a different sort of test called a faecal occult blood (FOB) test, which can be done at home. Doctors then use these test results to decide whether further investigation is needed. Colonoscopy is frequently used to investigate patients who have an abnormal FOB test result.
Nevertheless, this is a valuable study for policy makers in the UK. While the UK does not have a national colonoscopy screening programme in the same way as Austria, this study improves knowledge about the pattern of abnormalities found. A similar study of the UK programme could help identify if the same sex and age differences exist for people who are being investigated for signs of bowel cancer by colonoscopy after a positive FOB test.
Where did the story come from?
The study was carried out by researchers from the University of Vienna, Austria. Funding was provided by the Fund for Preventative Check-ups and Health Promotion.
The study was published in the peer-reviewed medical journal Journal of the American Medical Association (JAMA).
The coverage of this story was generally good with both the Mail and the Telegraph acknowledging that the UK does not have the same national screening programme as used in the study, but that the results may still be helpful. They also point out that both men and women are screened from 60 years of age in England, 10 years later than is the standard in the Austrian study.
Both reports also highlight that people in Scotland are already screened at a lower age (50 years) than in England and include quotes from the Beating Bowel Cancer campaign group who advocate lowering the age limit to 50 years of age across the entire UK.
What kind of research was this?
This was a cohort study using adult participants of a national screening colonoscopy programme over a four-year period (2007 to 2010) in Austria.
The researchers state that the typical age for screening for colorectal cancer (bowel cancer) in many countries (including the US and Austria) is 50 years for both men and women. The goal of bowel cancer screening is to find and remove abnormal growths in the bowel known as polyps. Once removed, the polyps can be tested in the lab to see if they are small and harmless (adenomas), slightly larger and potentially harmful (advanced adenoma), or already cancerous.
The authors say that previous research has suggested that men typically develop more advanced adenomas and have a higher prevalence of bowel cancer, so it has been suggested that men should be screened earlier than women should.
This research aimed to determine the correct age to screen men and women for bowel cancer.
What did the research involve?
This study followed 44,350 participants aged between 50 and 79 years old who were screened over a period of four years (2007 to 2010) as part of the national screening colonoscopy programme in Austria. Colonoscopy is the screening method used in Austria to detect early signs of bowel cancer. A colonoscopy is when a flexible tube attached to a small camera and light is used to examine your entire bowel.
The results of the colonoscopies, including laboratory tests, video and photo documentation, were reviewed for signs of adenoma, advanced adenoma and colorectal cancer (bowel cancer).
If more than one adenoma was found they were characterised (either as: harmless, potentially harmful or cancerous) by the most advanced one identified.
The researchers analysed their results in five-year age band separately for men and women. The prevalence and number needed to screen (NNS) were calculated. NNS was used to predict the number of colonoscopies that would need to be undertaken to detect one case of adenoma, advanced adenoma or bowel cancer. These were calculated separately for men and women at different five-year age bands ranging from 30-34 to over 95 years old. Most of those screened were aged between 50 and 79 years old.
This type of analysis is appropriate for this sort of study, and because it takes into account the different number of people screened in each age band, the NNS is a better assessment of the efficiency of the programme than the raw number of cancers detected.
What were the basic results?
A total of 22,598 (51%) women and 21,752 (49.0%) men were screened during the four-year period. The average age (median) for men and women was similar at 60.7 and 60.6 years respectively and ranged from 54.5 years to 67.6 years. Relatively few adults under 50 years old were screened.
Small abnormal growths (polyps) in the colon were found in 34.4% of individuals, colon cancer in 0.4% and rectal cancer in 0.2%.
Adenomas were found more frequently in men (24.9%) compared with women (14.8%) for all ages groups combined, suggesting that men have an extra 10% absolute risk of having adenomas. The prevalence of adenomas in 50 to 54-year-old men was 18.5%, significantly greater than the prevalence among women in the same age group, but similar to the prevalence among 65 to 69-year-old women (17.9%).
The NNS to detect adenomas was 4.0 (95% confidence interval [CI] 3.9 to 4.1) for men and 6.7 (95%CI 6.6 to 7.0) for women. In 50 to 54-year-old women, the NNS was nearly twice as high as the NNS in men of the same age (9.3 versus 5.4). The NNS among 45 to 49-year-old men (5.9) was similar to that in women aged 60-64 (6.0).
The prevalence of advanced adenomas was much higher in men (8.0%) than women (4.7%) for all age groups combined. The prevalence of advanced adenoma in men aged 50-54 (5.0%) was higher then women of the same age (2.9%) but was similar to women 10 years older (5.1%).
NNS to find an advanced adenoma were 21.5 (95%CI 20.3 to 22.8) for women and 12.6 (95%CI 12.0 to 13.2) for men.
The prevalence of bowel cancer was twice as high in men compared to women (1.5% versus 0.7% respectively) for all age groups combined. The number of colonoscopies needed to detect one case of bowel cancer was significantly lower in men compared to women for all ages combined (66.7 versus 137.0 respectively). The NNS in men who were 55-59 years old was again similar to women in the group 10 years older (75.0 versus 81.8 respectively).
How did the researchers interpret the results?
The authors concluded that being male was a significant risk factor in the development of bowel cancer, and that this indicates that ‘new sex-specific age recommendations for screening’ should be considered. They suggest that it may be important to start screening men earlier than 50 years to avoid early abnormalities being missed that could later develop into the observed higher prevalence of cancer in men. They also discuss the idea that women could be screened later due to their lower risk and prevalence of bowel cancer.
This study showed that the prevalence of adenoma, advanced adenoma and bowel cancer was significantly higher in men than in women of comparable age in Austrian adults taking part in a national colonoscopy screening programme.
This difference was shown using a large group of individuals within the age range that is currently screened for in Austria and the US. While the study’s size is a strength, it is important to acknowledge that it also has some limitations.
The study of prevalence only looked at differences in cancer prevalence between ages and sex. It did not look at whether other influences such as family history of bowel cancer, diet or ethnicity affected the age-sex relationship. Further studies with appropriate adjustment for these, and other potentially influencing factors, are warranted before the age-sex differences can be generalised with some confidence to different groups of people.
Only a relatively small number (n= 1,630) of people under the age of 50 years old were screened. Hence, the results obtained from these younger groups were more prone to uncertainty than larger, older groups.
This study tested screening for bowel cancer using colonoscopy; this is not the standard method in all countries. In England, Wales and Northern Ireland, patients over 60 years old are invited to be screened using a faecal occult blood (FOB) test kit that can be done at home. Those in Scotland can be screened from the age of 50 years old. The FOB tests for blood in the faeces. If blood is detected, an invitation of further investigation into the cause of the bleeding, which may include a colonoscopy, is made.
The age and sex differences for screening using the FOB test are not considered in this study and these findings are not as applicable to the UK as they would be to countries with a national colonoscopy screening programme such as Austria and the US.
This robust study provided important information about the difference in the prevalence of adenoma, advanced adenoma and bowel cancer in men and women of different ages taking part in a national colonoscopy screening programme in Austria.
While the UK does not have a national colonoscopy screening programme exactly like this, this study added to what is known about bowel cancer risk and the information may be valuable in helping policy makers make decisions about the future of the screening programme here.
- Ferlitsch M, Reinhart K, Pramhas S, et al. Sex-Specific Prevalence of Adenomas, Advanced Adenomas, and Colorectal Cancer in Individuals Undergoing Screening Colonoscopy. JAMA 2011; 306: 1289-1395
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