SIGGAR research summary

Overview

The Special Interest Group in Gastrointestinal and Abdominal Radiologists (SIGGAR) trials began in 2004 and were led by Professor Wendy Atkin (Imperial College London) and Professor Steve Halligan (University College London). SIGGAR comprised of two randomised controlled trials comparing three methods for diagnosing colorectal cancer.

The trial is an International Standard Randomised Controlled Trial, number 95152621.

Background

At the time of this study, colonoscopy was the gold-standard test for investigation of symptoms suggestive of colorectal cancer. Barium enema was widely available for diagnosis of colorectal cancer despite concerns about its accuracy and acceptability.

Computed tomographic colonography (CTC) was a relatively new alternative and less invasive diagnostic test. For investigating the large bowel, it was thought that CTC might be superior to barium enema and as good as colonoscopy. However, an important factor in establishing the feasibility of CTC as an alternative to colonoscopy was that additional tests after CTC were needed to confirm suspected colonic lesions.

The two SIGGAR randomised controlled trials aimed to compare the diagnostic efficacy, acceptability, safety and cost-effectiveness of CTC with barium enema and with colonoscopy.

Method

SIGGAR was parallel randomised controlled trials of barium enema compared with CTC and colonoscopy compared with CTC (randomisation 2 : 1, respectively). Patients with symptoms suggestive of colorectal cancer were recruited from 21 hospitals across England.

For the CTC vs colonoscopy trial, eligible patients were aged 55 years or older and regarded by their referring clinician as suitable for colonoscopy. Patients were randomly assigned (2:1) to colonoscopy or CTC by computer-generated random numbers, in blocks of six, stratified by trial centre and sex. We analysed the primary outcome – the proportion of patients referred for additional colonic investigation – by intention to treat. A secondary outcome was the detection rate of CRC and large polyps.

For the CTC vs barium enema trial, eligible patients were aged 55 years or older and regarded by their referring clinician as suitable for radiological investigation of the colon. Patients were randomly assigned (2:1) to barium enema or CTC by computer-generated random numbers, in blocks of six, stratified by trial centre and sex. We analysed the primary outcome – diagnosis of colorectal cancer or large (≥10 mm) polyps – by intention to treat. A secondary outcome was the proportion of patients referred for additional colonic investigation.

Other secondary outcomes for both trials were miss rates for cancer (via registry data), all-cause mortality, serious adverse events, patient acceptability, extracolonic pathology and cost-effectiveness.

Results and impact

A total of 8,484 patients were registered and 5,384 were randomised and analysed (barium enema trial: 2,527 barium enema, 1,277 CTC; colonoscopy trial: 1,047 colonoscopy, 533 CTC). Detection rates in the barium enema trial were 7.3% for CTC, compared with 5.6% for barium enema (p = 0.0390). The difference was due to better detection of large polyps by CTC (3.6% vs. 2.2%; p = 0.0098), with no significant difference for cancer (3.7% vs. 3.4%; p = 0.66).

Significantly more patients having CTC underwent additional investigation (23.5% vs. 18.3%; p = 0.0003). At the 3-year follow-up, the miss rate for CRC was 6.7% for CTC (three missed cancers) and 14.1% for barium enema (12 missed cancers).

Significantly more patients randomised to CTC than to colonoscopy underwent additional investigation (30% vs. 8.2%; p < 0.0001). There was no significant difference in detection rates of cancer and large polyps (10.7% for CTC vs. 11.4% for colonoscopy; p = 0.69), with no difference when cancers (p = 0.94) and large polyps (p = 0.53) were analysed separately. At the 3-year follow-up, the miss rate for cancer was nil for colonoscopy and 3.4% for CTC (one missed cancer).

Adverse events were uncommon for all procedures. In 1,042 of 1,748 (59.6%) CTC examinations, at least one extracolonic finding was reported, and this proportion increased with age (p < 0.0001). A total of 149 patients (8.5%) were subsequently investigated, and extracolonic neoplasia was diagnosed in 79 patients (4.5%) and malignancy in 29 (1.7%). In the short term, CTC was significantly more acceptable to patients than barium enema or colonoscopy.

Total costs for CTC and colonoscopy were finely balanced. CTC was associated with higher health-care costs than barium enema and the incremental cost per large polyp or cancer detected was £4,235 (95% confidence interval £395 to £9,656).

CTC was found to be superior to barium enema for detection of cancers and large polyps in symptomatic patients. CTC and colonoscopy were found to detect a similar proportion of large polyps and cancers and their costs were also similar. Guidelines are needed to reduce the referral rate after CTC. For most patients, however, CTC provides a similarly sensitive, less invasive alternative to colonoscopy.

The SIGGAR study findings are available in the NIHR-HTA Journals Library and were published in The Lancet in 2013 for the CTC versus colonoscopy trial and the CTC versus barium enema trial.