Who are at risk for familial colorectal cancer and how can they be managed?

The etiology of most cases of colorectal cancer is related to diet and lifestyle habits (see Chapters 2 and 4). However, in about 15% of cases, there is a family history of colorectal cancer and/or other malignancies (Figure 6.1). This includes a small number (<5%) where there is a recognizable dominant familial risk factor. In a larger number (>10%), there is a familial clustering of cancers and/or adenomatous polyps, which could be from a genetic susceptibility due to low-penetrance genes, or shared environmental-lifestyle risk factors, or an interaction between these two etiological causes. For an introduction to colon cancer genetics, see reference 1. References 1-3 provide an overview of the clinical features discussed below.