What is the case-control (CC) study?
The second study design included in the IARC report were case-control (CC) studies. One such study was by Erhardt et al. who conducted a CC consisting of 502 Caucasians investigating the association between alcohol, smoking, dietary factors and the risk of colorectal adenomas and hyperplastic polyps. The H.O.E. suggests that in high quality CC studies, the control group is similar to cases in every aspect except for the presence of the outcome. Erhardt’s CC lacks robustness as both cases and controls had adenomas, and the cases with adenomas had a higher body mass index (BMI) than controls. Further, a greater number of cases were smokers compared with controls. Similarly, patients with hyperplastic polyps had greater intakes of alcohol and cigarettes compared with controls. Shimizu et al. highlighted in his cohort that BMI, smoking, and alcohol are important. Had cases been similar to controls in all the above aspects, outcomes may have been different.
Millan et al. highlight the importance of age reporting 60% of CRC patients are & 70 years(yrs). Erhardt’ study was not randomly allocated but included participants who were within the selective age range of & 30yrs and 15g/d) is a risk factor for the development of hyperplastic polyps. However, this cannot be of certainty as the confidence interval is extremely wide (OR 3.70, 95% CI 1.49- 9.19). What’s more, the IARC study considered findings from this CC to be positively associated with CRC. However, Burnett- Hartman et al. argues that colorectal hyperplastic polyps are mostly identified as innocuous lesions. Therefore it is wrong to assume they will always progress to cancer.