UKFSST research summary

Overview

The UK Flexible Sigmoidoscopy Screening Trial (UKFSST) is a major research study that recruited over 170,000 people from across the UK. The principal aim was to examine the effect of a once-only flexible sigmoidoscopy screening on the future risk of developing colorectal cancer (also known as bowel cancer) and dying from this cancer.

This trial is registered with the ISRCTN Clinical Study Registry. Its unique number is 28352761.

Background

Colorectal cancer is the 4^th most common cancer in the UK and the 2^nd most common cause of cancer deaths. Survival is strongly related to stage at diagnosis, with survival rates of 90% for localised cases. Finding colorectal cancer early, or preventing its development, is an effective way to reduce deaths from this disease. Screening can potentially prevent colorectal cancers through the discovery and removal of bowel polyps: predominantly symptomless growths that have the potential to develop into colorectal cancer. Up to two-thirds of colorectal cancers are located in the rectum and sigmoid colon, which can be examined by flexible sigmoidoscopy.

At the time this trial was designed, flexible sigmoidoscopy had been shown to be safe, quick and accepted by patients. Theoretically, it was a strong candidate for a colorectal cancer screening test but evidence of its efficacy and long-term benefit was required. The role of the UKFSST was to assess the effect of once-only flexible sigmoidoscopy screening in people aged between 55-64 years old on incidence and mortality of colorectal cancer.

Method

Approximately 376,000 men and women were assessed for eligibility. They were aged 55-64 years old and were registered at one of 506 participating GPs between November 1994 and March 1999.

Of these, approximately 170,000 people said via a questionnaire that they would attend a flexible sigmoidoscopy test if invited and they were randomised. 41,000 people were screened by flexible sigmoidoscopy at the participating hospitals shown in the figure; the remaining people were not screened.

The study began in November 1994 and recruitment was completed by March 1999. Since 1999, we have continued to obtain health data from NHS data providers on study participants.

Results and impact

Our first analysis of longer-term follow-up was published in 2010 and showed that a once only flexible sigmoidoscopy screening reduced both the incidence and mortality from colorectal cancer. Incidence of colorectal cancer was reduced by 33%, and mortality by 43% in per protocol analyses. Confining results to the rectum and sigmoid colon, incidence was reduced by half in those who were screened. The protective effects of once-only flexible sigmoidoscopy also appeared to be long lasting with little attenuation of the protective effect over the 11 years of follow up. These results were published in The Lancet in 2010.

These compelling results suggested that offering once-only flexible sigmoidoscopy screening nationwide could significantly reduce the incidence and mortality of colorectal cancer. In 2010, the UK government announced a £60 million investment to introduce flexible sigmoidoscopy screening as part of the English NHS Bowel Cancer Screening Programme. Speaking at the introduction of flexible sigmoidoscopy to the screening programme, Harpal Kumar, then Chief Executive of Cancer Research UK said of the UKFSST:

“Cancer Research UK does not often use the word ‘breakthrough’ but this is one of those rare occasions when I am going to. It is extremely rare to see the results of a clinical trial which are quite as compelling as this. needs to be brought in as soon as possible. Every week of delay will risk scores of lives.”

Roll-out of flexible sigmoidoscopy screening began in 2013. It was estimated that screening could prevent up to 5,000 cases of colorectal cancer and up to 3,000 deaths from the disease in the UK each year.

In 2017, an updated analysis of the study showed that flexible sigmoidoscopy screening had a protective effect lasting at least 17 years. These results were published in The Lancet as well.

In addition to the original study objectives, we published a paper in 2020 that showed that having a better-quality flexible sigmoidoscopy gives greater protection against colorectal cancer.

However, in January 2021, flexible sigmoidoscopy was removed from the NHS Bowel Cancer Screening Programme in England. Despite its proven protection against colorectal cancer, a shortage of endoscopists meant that it was never fully rolled out across the whole of England. This was combined with disruption to the NHS during the COVID-19 epidemic, resulting in flexible sigmoidoscopy as a screening method being officially stopped in England.

In 2024, we published our findings that flexible sigmoidoscopy protects against colorectal cancer for at least 21 years. 32% of colorectal cancer cases and 36% of deaths from this disease were prevented by flexible sigmoidoscopy at 21 years in in per protocol analyses. These results were published in The Lancet Gastroenterology & Hepatology.

Over the life of the study we have also published many other papers on baseline findings and results of sub-studies. For a full list of these see ‘UKFSST results (publications)’.

We shall continue to follow the participants of the UKFSST to monitor the efficacy of flexible sigmoidoscopy for 25 years after the initial screening, until all participants will have had the opportunity to reach 80 years old. We also continue to analyse the data to answer many other questions around colorectal cancer, its development and how best to protect patients from it.