Prevention of bowel cancer: What’s new in screening methodology?
Colorectal cancer(CRC) is the 2nd leading cause of cancer death in Australia following lung cancer. CRC will develop in 5-6% of the adult population without family history and half will die as a consequence. Hence the importance for screening for CRC. Following table summarises risk groups and screening methods.
Formal guidelines have now been published early last year by American Society of Gastrointestinal Endoscopy(1) and by American Gastroenterological Association(2) in recognition of the findings (in multiple recent studies) that early detection of cancer and more importantly, the detection and removal of polyps which could become cancers, can decrease mortality from this disease.
Our main concern remains the prevention of bowel cancer in the average risk people without family history of cancer as well as for those who have history of bowel cancer in the first degree relatives since these two groups constitute the largest group of bowel cancers. Hereditary polyposis and hereditary nonpolyposis colon cancer syndrome constitute a minor part of the total number of bowel cancers diagnosed every year. The take home points from the American publications referred to above are as follows:
- Colonoscopy screening could reduce incidence of CRC by 58 to 86% and mor- tality by 64 to 90% ( data from six studies).
- Two large studies demonstrate that 5-6% of the population who are asympto- matic and do not have family history of bowel cancer had advanced lesions at screening colonoscopy. Hence the need to colonoscope average risk patients from the age of 50 and then every 10 years if the first colonoscopy is normal.
- In patients with one or two tubular adenomas less than 1 cm in size, 5 yearly colonoscopies are adequate.
- Sensitivity of Ba Enema in detecting polyps larger than 1 cm is 48% only( US National Polyp Study).
- Sensitivity of detection of larger polyps with CT/MR colonography varies between 40 to 96% reflecting wide variation in skills between different centres with high false positive rate of between 20-40%. One study concluded these not to be cost effective screening tools . Clearly these procedures did not have the therapeutic ability to remove polyps .
References:
1.Leiberman,D:Colon cancer screening:clinical Update(ASGE),10(3),Jan 2003. 2.Winawer,S etal:New guidelines on colorectal cancer screening and surveillance include major changes.AGA News:37(2)Feb 2003.