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 Cancer Genetics

Cancer is caused by genetic changes that lead to uncontrolled cell growth. While ALL cancer is genetic, most cancer is NOT inherited. Most of the time, these genetic changes occur during our lives due to random events.

Some families have a very strong history of cancer. In some of these families an inherited cancer predisposition gene is responsible for the cancer. The most common inherited cancers include breast, ovarian and colon cancer although other types exist.


As of July 1, 2011 the Ontario Breast Screening Program (OBSP) has expanded to include women aged 30 to 69 years at high risk for breast cancer at high risk screening centres across the province, including Trillium Health Partners - Credit Valley Hospital. Eligible women will be able to have annual MRI and breast mammography as well as genetic assessment and testing, if required, on referral by their physician.

The role of the Genetics team is to conduct a formal assessment of familial breast cancer risk, counseling and offer genetic testing if appropriate. Based on this consultation, screening recommendations are made.

For more information about the OBSP or how to refer a patient to the OBSP, please call 1 (800) 668-9304 or visit »


What to consider in your family history:

Trillium Health Partners - Credit Valley Hospital offers genetic counselling and where appropriate, genetic testing for individuals who may have an inherited cancer predisposition gene.

What to consider in your family history:

  1. The number of blood relatives on the same side of the family (mother’s or father’s) who have been diagnosed with cancer.
    Generally, if many relatives have had cancer, there is an increased chance genetics could be playing a role in the cause of the cancers. However, this is dependent on the size of the family. Smaller families may have fewer affected individuals.

  2. The age at cancer diagnosis.
    Generally, the younger the age at diagnosis, the greater the chance genetics could be playing a role.

  3. The type of cancer:
    Generally, if all the family members have the same type of cancer, there is an increased chance of a hereditary form of cancer. There are some different types of cancer well known to occur in the same person/family, such as colon and uterine cancer or breast and ovarian cancer.

  4. More than one cancer in the same person:
    Generally, if a person has had more than one cancer diagnosis, particularly in a different part of the body there is an increased chance of a hereditary form of cancer.

What to expect during a genetic counselling appointment:

All individuals referred to Genetics have their case reviewed by a Geneticist and/or Genetic Counsellor before the appointment.

You will meet with a Genetic Counsellor. During the appointment your family history will be reviewed. Genetic counseling involves education about the genetic mechanisms related to cancer. The genetic counsellor will provide a cancer risk assessment based on medical and family history. Options for genetic testing and recommendations for preventive screening and treatments will be discussed.

If indicated, genetic testing is offered, but only after the benefits, risks and limits of each test are carefully explained. Choosing if and when to have genetic testing is ultimately a very personal decision. Genetic testing is most often done on a blood sample. Another appointment will be arranged to go over the results of genetic testing.

How to make an appointment in Genetics

An individual requires a referral from their health care provider to be seen in Clinical Genetics. For more information, see How to make an appointment page»