The NHS bowel cancer screening programme

Dear Sir, We read with great interest the special article by West, Poullis and Leicester entitled ‘The NHS Bowel Cancer Screening Programme – a realistic approach with additional benefits’ in the September issue of Colorectal Disease [1]. The article provides a comprehensive background to colorectal cancer in UK, to screening in general and to the methods of screening for colorectal cancer currently available. However, the decision to use colonoscopy as the investigative technique in those individuals with positive faecal occult blood tests is based on data which are now 20 years old [2,3], and we feel that the NHS Bowel Cancer Screening Programme has missed an opportunity in the establishment of the programme to utilize more modern techniques to image the large bowel. Surely the investigation of choice in this group of patients should have been computerised tomographic (CT) colonography. There are ample data available now which suggest that this technique is at least as accurate, and possibly more accurate, than visual colonoscopy in terms of assessing the large bowel after adequate bowel preparation. Pickhardt et al. in 2003 [4] reported a series of 1233 patients who had undergone same-day visual colonoscopy and virtual colonoscopy using a 3D endoluminal display, with sensitivity rates of 93.8%, 93.9% and 88.7% for polyps at least 10, 8 and 6 mm in diameter, respectively, for virtual colonoscopy, compared with rates of 87.5%, 91.5% and 92.3% for visual colonoscopy. In the UK, Munikrishnan et al. [5] in the same year but in a much smaller cohort of patients, reported very similar efficacy rates for multislice CT colonography compared with colonoscopy in the detection of polyps and cancers > 6 mm in diameter. In a recent multi-centre study of 2600 asymptomatic individuals, Johnson et al. [6] reported a detection rate of 90% for CT colonography in polyps and cancers > 10 mm in diameter. However, CT colonography is mentioned briefly in the special article and then only as a fall-back investigation in those patients whose colonoscopy was inadequate or incomplete. Of those asymptomatic individuals with positive faecal occult blood tests who currently undergo colonoscopy, approximately 50% will have significant pathology (either polyps or cancers); these patients would therefore still require colonoscopy had their screening test been CT colonography rather than visual colonoscopy, assuming that their pathology was detected by CT initially. However, the remaining 50% would potentially be spared visual colonoscopy on the basis of a normal CT colonography. While there is no doubt that the NHS Bowel Cancer Screening Programme has been partly responsible for driving up standards in colonoscopy, a requirement for 50% fewer extra colonoscopies probably would have had much the same effect in the long run. It could also be argued that the use of CT colonography as the primary screening modality might have a similar effect in terms of driving up standards of CT colonography and its reporting. Furthermore, CT colonography has the potential for the detection of other, extra-colonic pathology, much of which may be inconsequential, but some of which (e.g. asymptomatic aortic aneurysms) may be very significant [7,8]. The risks of colonoscopy are well documented [9]; current assessment of the risks associated with radiation exposure during CT colonography, allowing for recent improvements in technology, suggests that the risk is nonexistent or too small to measure, according to the Health Physics Society [10]. Furthermore, when exposed to all possible techniques currently in use for colonic surveillance, and asked to express a preference, patients preferred CT colonography to both barium enema and colonoscopy, based largely on the amount of pain experienced during the procedure [11,12]. The introduction of narrow band imaging to visual colonoscopy may change the balance of benefit in favour of visual colonoscopy against CT colonography in the future, but currently patients should be offered the choice. The concept of ‘informed consent’ implies that all diagnostic or treatment options are discussed with the patient before he or she can reasonably be expected to make an informed decision about the future direction of his or her health care. CT colonography is one of the diagnostic modalities which ought to be discussed with patients presenting with positive faecal occult blood tests; we would anticipate that the vast majority of such patients would choose CT colonography rather than colonoscopy, in the knowledge that approximately 50% of them would still require a colonoscopy eventually. These patients are not being given sufficient information on which to base their decisions; perhaps it is time to re-think this approach.