ObeSity Related Colorectal Adenoma Risk

Bowel cancer, or colorectal cancer (CRC), is the second most common cancer affecting both men and women in England. The majority of CRCs develop from a pre-cancerous type of growth in the bowel called an adenoma. Detecting and removing these adenomas is important in reducing CRC risk. A study which undertook a once-off camera examination of the left hand side of the bowel (flexible sigmoidoscopy), removing any adenomas, demonstrated a reduction in CRC by 23% and reduced mortality by 31%.

Although a single cause for adenomas is not known, several factors can predispose patients to adenomas, including; age, gender, family history, cigarette smoking and excess body weight (EBW).

Obesity is becoming an increasing problem in the UK, with approximately a quarter of adults classed as obese in England. Patients who are obese are at higher risk of having adenomas. Studies have shown that patients with EBW are more likely to have fatty disease of the liver (non-alcoholic fatty liver disease, NAFLD) by laying down fat in the liver. Studies in Asia have shown that patients with NAFLD are more likely to have adenomas, and that these are more likely to be in the right side of the bowel which is furthest from the anus (right colon). Although these studies have shown a link between NAFLD and adenomas, they have all used invasive or expensive markers of fatty liver disease. No study has correlated the link between liver enzymes (blood tests) and adenomas or by using scoring systems to determine the presence or absence of significant fatty liver disease. Furthermore, no Western studies have confirmed the link between NAFLD and adenomas, meaning it is unclear whether this link is only present in the Asian population.

Approximately 400,000 colonoscopies (camera examinations of the large bowel) are performed each year within the NHS for the investigation of gastrointestinal symptoms, including: altered bowel habit, rectal bleeding and low blood count. When polyps are found, patients often have a follow-up surveillance colonoscopy to check that no new adenomas have formed. The timing and need for surveillance is based only on the number and size of adenomas found and does not take into account any risk factors which the patient may have.

The NHS Bowel Cancer Screening Programme (BCSP) invites all individuals aged 60-74 to undertake a stool sample test which looks for blood, called faecal occult blood testing (FOBt), every two years. Those who have a positive FOBt are then invited for a colonoscopy. This programme is purely based on age and is not targeted. Another arm of the BCSP was introduced in 2013, where all individuals aged 55 are invited for a flexible sigmoidoscopy and removal of adenomas. Anyone who is felt to be high risk according to the number or size of adenomas then undergoes a colonoscopy.