PHOENIX — Of all colorectal and breast cancer cases, 5%–10% are linked to hereditary causes, according to a Mayo Clinic review of the most commonly encountered hereditary syndromes and conditions.

These high-risk hereditary predisposition syndromes have been associated with a markedly increased lifetime risk of cancer, some approaching 100%, says Niloy Jewel Samadder, M.D., a gastroenterologist in the Department of Clinical Genomics at Mayo Clinic's Arizona campus. This makes genetic testing critical to early detection of cancer risks and decisions on surveillance and treatments.

"Genetic testing has become a key tool to help identify syndromes and conditions that predispose a person to gastrointestinal and breast-ovarian cancer," says Dr. Samadder, lead author of the study published in June in Mayo Clinic Proceedings. "Identifying these patients through family history and genetic testing allows physicians and patients to talk about cancer risks, and make decisions about appropriate screening, surveillance and interventions."

The study recommends referring for genetic testing patients with no personal history of cancer but with a family history of early onset (before age 60) of breast, ovarian, endometrial or colorectal cancer. Patients with certain established malignancies also should be further assessed for hereditary syndromes.

Two other patient profiles suggest a need for genetic testing: the clustering of multiple cancers in two or three successive generations and the presence of certain rare tumor types, including ureteral cancers and diffuse gastric cancer.

Though many people may think genetic testing is complicated or unnecessary, the tests are performed easily, most often on a blood sample or saliva swab, Dr. Samadder says. The tests aren't always conclusive in terms of clinical implications, but they're continually improving to establish diagnosis and identify at-risk patients.

A personalized genetic risk assessment, which incorporates family histories and statistic models, can further estimate a patient's risk of developing cancer due to an inherited genetic mutation. For patients who have an identified hereditary breast-ovarian cancer syndrome and who chose not to have risk reduction surgery, enhanced surveillance is essential. Earlier breast screening is recommended, with clinical exams recommended every six months, beginning at age 25.

Screening for ovarian cancer is more difficult, since currently available tests, including transvaginal ultrasound, perform poorly, the Mayo review says. Among considerations for reducing risks is use of oral contraceptives, which research has shown reduce the risk of ovarian cancer by nearly 30% in the general population and may be even more effective among patients with identified hereditary risk. "Thus, oral contraceptive use may be considered to prevent ovarian cancer in high-risk women," the study says.

The most common hereditary colorectal cancer syndrome — Lynch syndrome — represents 2%–4% of all colorectal neoplasias, which are abnormal cell growths that can include tumors. Patients identified as having Lynch syndrome have a marked increase in lifetime risk of developing colorectal cancer or endometrial cancer, as well as a predisposition to other cancers. These patients should undergo close colorectal cancer surveillance, with colonoscopy every one to two years, in addition to screening for gastric, gynecological and urinary tract malignancies.

With early genetic evaluation of a hereditary predisposition to this and other cancers, the patient's health care team can develop a coordinated approach to screening and prevention, Dr. Samadder says.

"By identifying patients and families who would benefit from a genetics evaluation, we can improve screening, early detection and prevention of cancer," he says.

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About Mayo Clinic Proceedings 
Mayo Clinic Proceedings is a monthly peer-reviewed medical journal that publishes original articles and reviews dealing with clinical and laboratory medicine, clinical research, basic science research, and clinical epidemiology. Proceedings is sponsored by the Mayo Foundation for Medical Education and Research as part of its commitment to physician education. It publishes submissions from authors worldwide. The journal has been published for more than 80 years and has a circulation of 130,000. Visit the Mayo Clinic Proceedings website to view articles.

About Mayo Clinic 
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Media contact:

• Joe Dangor, Mayo Clinic Public Affairs, 507-284-5005, newsbureau@mayo.edu

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