Oncogenetics

Your physician has referred you to oncogenetics because he has reason to believe that you are at increased risk of developing one or more types of cancer during your lifetime. This is called a genetic predisposition to cancer. A person who is genetically predisposed to cancer will be more closely monitored to prevent or detect cancer, if necessary. 

Oncogenetics consultation

Getting a consultation in oncogenetics

Your physician must first refer you to oncogenetics. He will explain the reason for his referral; otherwise, a member of the genetics team will do so.  


Each consultation request is evaluated. The medical geneticist evaluates every incoming consultation request and assigns each a level of priority. The waiting period for a consultation varies from person to person and according to the urgency of each case.


Your medical file and your family history will be analyzed. A genetics counsellor or a medical geneticist will analyze your medical file and your family history to assess the likelihood that you are genetically predisposed to cancer. If you present a risk greater than that of the general population, we will recommend one or more genetic tests. If the tests confirm that you are genetically predisposed, some of your relatives may also be selected for testing.


When it is clear that a person is genetically predisposed to cancer, we can offer adapted cancer screening options and/or management (e.g.: treatment or surgeries) to lower the risk of cancer.


An appointment in oncogenetics is a medical consultation, not recruitment of candidates for a research project.  
 

Preparing for your appointment in oncogenetics

A worker at the appointment centre will contact you to schedule an appointment. You are invited to complete the family history information-gathering tool (below) and to watch the video (below) to prepare for the meeting. 


Family information-gathering assistance tool (French)
 

What you need to know about the oncogenetic consultation

The oncogenetic consultation will be either by phone or by hospital appointment.


Have your family cancer history information ready (family history information-gathering tool (french)), your health insurance card and your hospital card.


The meeting will last 30 to 45 minutes. The objective is to assess your genetic risk and predisposition to cancer and to explain potential tests to you. This meeting is an opportunity to discuss your concerns about your family history of cancer and your visit in medical genetics. If you wish, you may be accompanied by other family members for a consultation.


During the meeting, we will draw up your family tree. We will ask you questions regarding your health and perform a physical examination, if required. In order to provide a better assessment, it is sometimes necessary to obtain further information that is contained in the medical files of your relatives (e.g., types of cancer that they had). If that is the case, the relatives concerned must give their written consent. We will provide you with the requisite form, if necessary. 
If you have a genetic predisposition risk greater than that of the general population, genetics experts will recommend medical genetics tests. The decision to proceed with these tests is entirely yours. The genetics counsellor and the medical geneticist will assist you in making an informed and enlightened decision. Many elements can guide your decision, including:


•    the efficacy of the preventive or cancer-screening methods;
•    anxiety;
•    the possibility of an inconclusive result;
•    the desire to prevent disease among relatives;
•    social and family pressure.


Please note that genetic test results are kept in the user's medical file as are any other results. The results can influence the insurability of those who consult.

You may need time to reflect before proceeding with the tests. No matter what decision you make, the medical geneticist will recommend monitoring that is adapted to your needs and that of your relatives.
 

To pass a medical genetics test

Genetic tests may be performed on cancer tissue kept at the hospital or on a blood sample. Blood samples are usually taken at the screening centre on the day you choose following the consultation.


The wait time for genetic test results is one to four months. The results will be given to you during a follow-up consultation, in person or during a phone call.
Genetic testing will attempt to shed light on whether or not you are genetically predisposed to cancer. We look for genetic variations, commonly known as genetic mutations. There are two types of situations:

  • Search for family genetic variation: If a variation in your family is already known, only that specific genetic variation will be sought.
  • Gene panel: In the absence of known genetic variations within the family, we will proceed with a more in-depth investigation (one or more genes) based on the types of cancer you or your relatives have had.

Understanding your results

Negative test result

  • Family genetics investigation: The family genetic variation has not been identified. The result means that the person tested has not inherited the mutation identified in a blood relative. The risk of having cancer is therefore similar to that of the general population. 
  • Gene panel: No mutation has been identified through genetic testing. This does not exclude genetic predisposition to cancer by 100%. You may still have a genetic mutation that has not been identified in the tests, either for technical reasons or because some causes of genetic predisposition to cancer have not yet been discovered. Your risk of cancer and the monitoring recommendations will be estimated based on family history.  

Positive test result

A positive test result means that a genetic mutation has been identified. Targeted screening is recommended according to the risks of developing particular types of cancer associated with the mutation. It is sometimes possible to elect preventive surgery.

Depending on the mode of transmission of the genetic predisposition, the genetics counsellor will inform you about those who are at risk in your family. These persons may take a predictive gene test if they so wish. 

The predictive gene test is offered only after a consultation in genetics. A referral from a physician is required.

Receiving a positive result may sometimes come as a shock. The medical geneticist and the genetics counsellor will guide you to the appropriate resources in accordance with your needs.

Inconclusive test result

A genetic test may occasionally identify a genetic mutation whose clinical significance is inconclusive. This means that it is difficult to determine precisely whether or not the genetic variant has a significant effect on health.

When there is an inconclusive result, a follow-up appointment in genetics is held. It may be recommended that other family members be tested to determine whether the genetic variant has an impact on health. It is also important to contact the genetics department again in the subsequent years to keep pace with the progress of scientific knowledge.

Learn more about medical genetics

See the medical genetics page for additional information.

The genetic foundations of cancer

There are many types of genetic predisposition to cancer, also known as family cancer syndromes. 


Further information about genetic predisposition to cancer is available below.

Cells, genes and DNA

The human body is composed of billions of cells. They are the basic unit of all living organisms. 

Every cell has a nucleus containing DNA. DNA varies from one individual to the next. It is a combination of both parents’ own DNA. DNA contains four base letters: A, C, G and T. The letter sequence provides the cell with instructions on how to complete its functions. The DNA sequence is known as the genetic code and the instructions in the sequence are referred to as genes.

Consult the medical genetics page. 

The concept of genetic variation (mutation)

The human genetic code contains approximately 20,000 genes. A variation is a sequencing error in the letters of a gene or a DNA strand. It is like a spelling mistake. Some variations can lead to health problems; others are benign and do not affect health.

DNA contains two copies of each gene. Each parent transmits one of two copies of each gene to his/her child. For every gene given, the child receives a copy from his mother and another one from his father.

In some cases, a single copy of a mutated gene can result in disease or a genetic syndrome, whereas in others, both copies must mutate. The former case is referred to as dominant inheritance while the latter is known as recessive inheritance. Most family cancer syndromes are dominant inheritance. A child will have the syndrome if he has a copy of the carrier parent’s gene.

How cancer occurs

According to the Knudson hypothesis (or two-hit hypothesis), cancer requires at least two DNA genetic variations within a cell. The variations may be inherited from the parents. They are therefore present at birth in all of the body’s cells. This increases your risk of developing cancer.

Other genetic variations may occur spontaneously throughout one’s lifetime. They are known as acquired variations and may occur randomly (e.g., during cellular division). Aging may be behind some of these variations.

Acquired variations are not transmitted to the next generation.

Cells may become cancerous when variations accumulate in DNA and when the genes that monitor and repair errors or control cell growth and division malfunction. Cancerous cells then actively multiply at a variable speed until they form a malignant tumour or cancerous mass.

Sporadic and hereditary cancers

Random or acquired variations following exposure to environmental risk hazards are referred to as sporadic cancers. Two acquired variations must occur, specifically one in each copy of the same gene, for a person to develop a sporadic cancer.


Hereditary cancer occurs when the patient has a family cancer syndrome. At birth, the person a variation among all of his cells that increases the risk of developing cancer.


If an acquired variation expresses itself in the other copy of an already mutated gene, the carrier may develop cancer. Only 5% to 10% of cancers are hereditary.
 

Examples of family cancer syndrome

Colon cancer (e.g., Lynch syndrome) 


Lynch syndrome is associated with a greater risk than the general population of having colon and endometrial cancer (endometrium: inner mucus of the uterus). There is a risk of developing other types of cancer associated with Lynch syndrome including: stomach, ovarian, small intestine, biliary tract, bladder, brain, pancreatic, and sebaceous gland.

Lynch syndrome can also be caused by mutations found primarily in four genes: MLH1, MSH2, MSH6, and PMS2. Further analyses of cancerous tissue may be provided before proceeding with a genetic test of the blood if Lynch syndrome is suspected. When the complementary analyses are abnormal, a blood sample is used to seek a variation in one or more genes associated with Lynch syndrome.
Lynch syndrome is dominant hereditary, meaning that the children of one of the carriers of the genetic variation of one these four genes each have a 50% probability of inheriting this variation and of being at risk of developing a cancer associated with Lynch syndrome.

There are other, rarer syndromes associated with a greater risk of colorectal cancer. Familial adenomatous polyposis, recessive polyposis (MUTYH), juvenile polyposis syndrome, and Peutz-Jeghers syndromes are four examples.


Hereditary breast and ovarian cancer 


Hereditary breast and ovarian cancer syndrome means there is an increased risk of breast and ovarian among women and of prostate cancer among men. It is also associated with a slightly greater risk of melanoma and of pancreatic cancer.

BRCA1 and BRCA2 are the two best known genes associated with this syndrome. As with Lynch Syndrome, breast and ovarian cancer syndrome is dominant hereditary, so there is a one in two (50%) risk that each child has received the syndrome from the carrier parent. 

Breast cancer may be caused by reasons other than genetic syndromes. Li-Fraumeni syndrome and Cowden syndrome are two examples.
For further information on hereditary breast and ovarian cancer syndrome, consult the following section: Further resources
 

Further resources

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