Hereditary Cancer Genetics
This page was last updated on May 14, 2025.
A diagnosis of cancer is common but hereditary cancer is not. Most cancers develop by chance. About 5 to 10% of cancers are hereditary. We all have genes that protect us from developing cancer. If you are born with a change (called a mutation) in one of these genes, you have an increased risk of developing certain types of cancer. This is called hereditary cancer. Mutations can be passed down from your parents and passed on to your children.
You may be referred to a Genetics Clinic for genetics counselling if you or your family have:
- Many family members with cancer, especially the same type or related types of cancer.
- A family member with ovarian cancer at any age.
- A family member with more than one cancer (for example: a woman with breast and ovarian cancer).
- Family members with cancer under the age of 50.
- Family members with rare cancers (for example: breast cancer in a person assigned male at birth).
- A family history of a known hereditary cancer gene mutation (examples: BRCA1/2, APC).
Referrals for Genetic Counselling
You should be referred for genetic counselling if you have a personal and/or family history suggestive of an inherited predisposition to cancer. You need to be referred by a member of your healthcare team. The Genetic Testing for Hereditary Cancers handout may be provided to you when the referral is submitted.
For more information, read Ontario Health’s Referral Guidance for Hereditary Genetic Assessment
Preparing for Your Genetics Clinic Appointment
Preparing for Your Genetics Clinic Appointment
Having information on your family’s history of cancer is needed to complete your assessment. You may be asked to complete these forms in advance of your Genetics Clinic appointment:
If any family member has had genetic testing completed, ask them for a copy of the results and bring it to your appointment. You may be asked for this in advance of your appointment. This is especially important if family members have been identified as carrying a harmful change in a hereditary cancer gene (examples: BRCA1, BRCA2). We need the information from their genetic testing report in order to arrange genetic testing for any family member.
During your appointment in the Genetics Clinic, genetic testing may be offered to you or suggested for your family members. For some people, genetic testing may be offered directly by an oncologist or surgeon before their genetics appointment. You do not have to have Genetic testing. Genetic testing may help guide your choices for treatment. It may also give you and your family useful information about your future risk of cancer and what cancer screening you may need. Some people who do not qualify for provincially covered genetic testing may choose to pay for testing. Read the Private Pay for Genetic Testing handout.
High-Risk Ontario Breast Screening Program (OBSP)
You may be eligible for high-risk breast cancer screening through the OBSP if you have a strong family history of breast cancer. The high-risk program offers annual breast screening by mammogram and breast MRI to women between the ages of 30 and 69 who have at least a 25% lifetime risk of developing breast cancer. Screening results are sent back to your primary care provider. Follow-up care is arranged through their office.
Go to the Breast Cancer Screening for People at High Risk page on Cancer Care Ontario's website for more information on who is eligible for high-risk breast cancer screening. Ask your family doctor or nurse practitioner for a referral to this program if you meet criteria for screening.