Cigarettes decisively linked to colorectal cancer

13 Feb 2008

Cigarette smoking is a well established risk factor for many tumour types including lung, oral cavity, kidney, pancreas, esophagus, and stomach. Although several studies have suggested that cigarette smoking has a marked effect on the development of adenomatous polyps, the association between cigarette smoking and colorectal cancer (CRC) has been more controversial, and smoking is not currently listed as a risk factor for CRC by the International Agency for Research on Cancer.

Adenomatous polyps are relatively common in the general
adult population, and most, if not all, CRCs develop along an
adenoma-carcinoma pathway. As a result, adenomas are frequently used as a surrogate endpoint in epidemiologic studies of risk factors for CRC.

In the latest issue of Gastroenterology, Botteri et al. present the results of a meta-analysis, based on 42 independent studies, evaluating the association between cigarette smoking and adenomatous polyps of the colon. The authors compared the effects of smoking with the likelihood of developing high-risk adenomas (i.e. „d1 cm in diameter, villous components, severe dysplasia) . The association between smoking and adenomatous polyps was greater for high-risk adenomas than for low-risk adenomas.

The controversy in the association between cigarette smoking and CRC is often explained by the latency period to uncover an association between cigarette smoking and CRC. The authors of this paper discuss another possibility: The inclusion of a high proportion of subjects with adenomas in the unscreened control groups of most CRC case-control studies. Given the consistent association found between smoking and adenoma, the misclassification of controls might result in a significant decrease of the observed associations between smoking and CRC risk. In this new study, Botteri et al. have reinforced the association between smoking and adenomas, while presenting constructive reasons for the weaker associations observed in prior studies of smoking and CRC.