The visual test identifies abnormalities in the bowel
A new bowel cancer test “cuts deaths by 40 per cent”, according to The Daily Telegraph. The newspaper estimates that offering the brief, one-off test to people aged 55 could save 3,000 lives a year and prevent a further 5,000 people from developing bowel cancer.
Several other newspapers also reported the results of a well-conducted, landmark trial into the screening test, which involves inserting a flexible camera into the bowel to check for abnormal growths (polyps) that may become cancerous. Those who attended screening were 33% less likely to develop bowel cancer and 43% less likely to die from it than those not invited for screening.
Several aspects of this test need consideration, such as the relatively low uptake rate (only 53% of those who were approached attended screening) and the invasive method used. However, bowel cancer is the third most common type of cancer in England, affecting around 31,000 people and causing around 13,000 deaths each year. Given this test’s potential to save thousands of lives through early treatment, its overall benefits seem clear.
Those who attended their invited screening session (i.e. disregarding those who did not attend) had a 33% lower risk of a colorectal cancer diagnosis than those in the control group (HR 0.67, 95% CI 0.60 to 0.76). Screening attendees also had a 43% lower risk of death from colorectal cancer (HR 0.57, 95% CI 0.45 to 0.72). The researchers report that the incidence of colorectal cancer in non-attendees was very similar to that in those not invited (the controls).
The researchers calculated that 191 people needed to be screened to prevent one colorectal cancer diagnosis by the end of the study period. To prevent one death from colorectal cancer, 489 people would need to be screened.
How did the researchers interpret the results?
The researchers concluded that “flexible sigmoidoscopy is a safe and practical test”. They say that offering a single test between the ages of 55 and 64 “confers a substantial and long lasting benefit”.
This well-conducted, landmark trial investigated the effect of inviting healthy adults with an average age of 60 to attend a one-off lower-bowel examination, using flexible sigmoidoscopy, to screen for cancer.
Colorectal (large bowel) cancer is reportedly the third most common cancer worldwide and accounts for 600,000 deaths every year. As cancerous and pre-cancerous bowel growths are often symptomless in the early stages, visual detection during this early stage may be expected to reduce diagnoses of cancer and deaths due to the cancer.
The strengths of this study include the large number of people included in the trial and the average 11-year follow-up. While only 1.5% of the participants included developed colorectal cancer and only 0.43% died from it, the study’s sample size was sufficiently large to offer a reliable statistical comparison of the screened and unscreened groups. This trial has demonstrated that inviting people to screening reduces their risk of being diagnosed with colorectal cancer by 23% and their risk of dying from colorectal cancer by 31%. If they attend screening when invited, their risk reduction is even greater (respectively 33% and 43%, the higher figures quoted by the media).
An important and unavoidable obstacle to a screening programme is uptake of the test among the general population. The NHS already has a bowel-screening programme in place, which offers screening to all men and women aged 60 to 69 every two years. This involves sending out a “faecal occult blood test kit” to use at home and send back for analysis. The screening test detects small amounts of blood in faeces (invisible to the naked eye) which, if present, may be due to the presence of polyps or tumours that need further examination (often using colonoscopy). The pilot study that led to the introduction of the current screening programme found uptake in the pilot population to be about 57%.
The invasive nature of this new screening examination may be unacceptable to some people. This trial only included people who responded “yes” when asked if they would attend bowel screening if invited. Only 52.9% of them said yes, and they were subsequently invited. Of these people, only 71% attended when sent an appointment. From this experience, uptake in the eligible population as a whole could potentially be lower than 50%. Uptake and other important factors relating to screening, including possible anxiety associated with the screening process and waiting for results, will need to be carefully considered whenever a new programme is introduced or changes are made to an existing one.
The importance of these findings should not be underestimated, and the potential benefits of this screening programme are worthy of serious consideration. As the chief executive of Cancer Research UK said: “This is one of those rare occasions to use the word breakthrough. It is extremely rare to see clinical trial results as compelling as these.”