Detect InSpect ChAracterise Resect and Discard 2

Colorectal cancer (CRC) continues to be a major problem in the UK and is the second most common cause of cancer death. The annual incidence is approximately 30,000 cases with an annual mortality rate of in the region of 16,000 (1). Most sporadic non-hereditary CRCs arise from benign colorectal adenomas (2). The detection and resection of colorectal adenomas at colonoscopy has been shown to reduce the subsequent risk of CRC by as much as 80% (3).

The NHS Bowel Cancer Screening Programme (BCSP) began roll-out in 2006 in England and as of April 2010, was established across 99.4% of the country. The BCSP is based on a strategy of biennial faecal occult blood test (FOBt) screening for men and women aged 60-75, followed by colonoscopy for those who test positive. Among its aims is the detection and resection of potentially pre-malignant colorectal adenomas thereby potentially reducing the incidence of CRC. The introduction of the BCSP has resulted in a dramatically increased demand for colonoscopy. To date approximately 80,000 colonoscopies have been performed within the BCSP and at least one adenoma found in just under half of the procedures (4). In addition, from 2012, the BCSP will introduce flexible sigmoidoscopy screening for all individuals aged 55 yr olds. This extrapolates to approximately 500,000 flexible sigmoidoscopies per year, with at least one polyp expected to be found in 75,000 procedures.

Greater than 90% of polyps detected at colonoscopy are small (6-9mm) or diminutive (≤5mm), with the latter making up the majority (5-7). In addition, approximately 50% of small polyps are non-neoplastic (8), known as adenomas. The number of adenomas present strongly influences the future risk of the development of advance neoplasia for the individual patient and therefore determines decisions on future surveillance intervals. As a result even small polyps, with little risk of harbouring cancer, are currently sent for histological assessment in order to determine whether or not they are adenomatous (9-11).

The ability to correctly diagnose a small polyp (< 10mm) during colonoscopy as adenomatous or non-adenomatous from its endoscopic characteristics (optical diagnosis) would allow small adenomas to be resected and discarded without the need to retrieve the polyp for formal histological assessment. Additionally, hyperplastic rectosigmoid polyps can be left in situ thereby reducing the need for polypectomy and the associated risks. Optical diagnosis would also enable surveillance intervals to be determined immediately after colonoscopy thereby avoiding the need for out-patient follow up, potentially leading to significant time and cost savings. Notably, histological assessment is an imperfect current gold standard as polyps may be lost or be unable to be assessed due to diathermy artefact in 8-25% of cases. Furthermore, standard histological techniques may misclassify up to 15% of adenomas as benign lesions.

Narrow band imaging (NBI; Olympus, Japan (12, 13)) is a new 'blue light' optical imaging modality available at a push of a button on the colonoscope head. By enhancing mucosal detail and in particular vascular structures it allows assessment of microvascular density (vascular pattern intensity - VPI (14); meshed brown capillary network (15-17)). Neoplastic tissue is characterized by increased angiogenesis and, therefore, adenomas appear darker when viewed with NBI. The use of microvascular assessment appears to have a short learning curve, as short as 60 histologically verified polyps (18-20), making it a potentially attractive and practical option for optical diagnosis. There are no known adverse events associated with NBI.