Genetics & Colorectal Cancer

By Puneet Singh Cheema, MD, HealthEast Cancer Care Medical Director

Family history is one of the most important risk factors for colorectal cancer. Nearly one-third of colorectal cancers are attributable to hereditary factors. Moderate-risk genes and the interaction of these genes with lifestyle and environmental factors contribute to the development of more than 25% of colorectal cancers. In addition, an estimated 5% of colorectal cancers are due to the inheritance of single, strongly predisposing genes for which genetic testing is currently available.

Family history

Family history influences risk-reduction strategies. Guidelines suggest earlier and more frequent screening when there is a family history of colorectal cancer. The age to begin, frequency, and method of screening depends on the number of family members with cancers, the ages at diagnosis, and how closely related they are. Screening for other cancers is needed for some genetic conditions.

Predisposition to colorectal cancer

The most common colorectal cancer predisposition syndromes occur via two pathways. Polyposis syndromes elevate risk due to an increase in the number of polyps. Polyposis is readily identifiable due to the physical clue of multiple polyps. Nonpolyposis syndromes elevate risk because the polyps that do occur progress more rapidly to cancers. Nonpolyposis syndromes are more difficult to identify because of the absence of large numbers of polyps, and must be identified through family history or by tumor features.

Genetic counseling and testing

Genetic counseling and testing is offered through the HealthEast Cancer Genetics Clinic, and is offered to patients with signs of hereditary risk. The goal of genetic counseling is to provide information about hereditary risk, management of hereditary risk, and options for clarification of risk via genetic testing. Genetic testing helps to clarify risk for colorectal and other cancers, and thus directs screening strategies. Features of hereditary risk include early onset of cancers, multiple primary cancers in an individual, family history of colorectal and other cancers, and specific tumor characteristics. HealthEast is developing a program to systematically identify individuals at risk for hereditary cancers via examination of tumor pathology features.

Next: Colorectal Cancer Data