A prospective study of faecal bile acids and colorectal cancer

A prospective study of 7079 people aged 45-74 recruited through general pra ctices in South Wales, Herefordshire and Edinburgh, Scotland was undertaken to test the hypothesis that faecal bile acids are implicated in the causat ion of large bowel cancer. The population was recruited between 1974 and 19 80 and the response rate for stool collection was 67%, Bile acid analyses w ere performed on those cases that presented by 1990, It was decided in adva nce to examine the hypothesis separately for left- and right-sided bowel ca ncer because of known epidemiological differences between the two sites and to exclude the cases presenting within 2 years of the stool sample from th e analyses because the cancer could have been present at recruitment and mi ght have possibly affected faecal bile acid concentrations. Each case (n = 51 left-sided and 8 right-sided) was matched with three controls by age (wi thin 5 years), sex, place of residence and time of providing the stool samp le (within 3 months). Statistical analyses using conditional logistic regre ssion showed no significant differences between the left-sided cases and co ntrols for any of the concentrations of individual bile acids, total bile a cid concentrations, faecal neutral steroids, percentage bacterial conversio n and the ratio of lithocholic acid to deoxycholic acid concentrations. The re was a statistically significant (P = 0.021) association of the presence of chenodeoxycholic acid (5/8 samples) in the right-sided cases compared wi th the controls (3/23), odds ratio 6.26 (95% confidence interval 1.19, 32.8 4). A high proportion of primary bile acids has also been found in other st udies of patients with a genetic predisposition to proximal bowel cancer, h owever this pattern may also occur in low risk groups, such as Indian veget arians, suggesting that they may predispose to right-sided bowel cancer onl y in the presence of other, as yet unknown factors. If bile acids are invol ved in the causation of large bowel cancer, they may be part of a complex s et of interacting factors. (C) 2000 Lippincott Williams & Wilkins.