The rightward shift of colon cancer. Aging or artifact?

The results of a cross-sectional study were recently used as the primary basis for postulating a causal relationship between aging and the observed increasing proportion of right-sided colorectal carcinoma diagnosed in recent decades. However, cross-sectional research methodologies are more prone than cohort designs to biases that may produce misleading results, especially those biases due to differences in disease detection and in patient losses among study groups. A hypothetical prospective cohort model is used to help illustrate these methodological limitations. Other data reviewed appear not to support the "aging gut" hypothesis. Additional information using more robust methodologies will be needed to delineate the role of aging in the shift in location of colorectal carcinoma.