Our genetic profile can influence our response to certain treatments or the type of treatment that will be offered. We present to you some applications of precision medicine in relation to the medication or the choice of treatment.
Pharmacogenomics is how a person’s genetic variations affect their response to medications. The results of this test can help guide medication selection to reduce trial-and-error. They can help assess which medications may provide the most benefit and which medications carry the risk of side effects.
- Pharmacogenomic testing is currently limited to a small number of medications and health conditions, and may not apply to you. Moreover, genetic variations are not the only factor influencing the response to medications.
Precision medicine also affects genetic changes that are acquired during our lifetime and which are therefore not hereditary. Here are two examples of where precision medicine is used when a person has cancer.
Targeted Treatments for Certain Cancers
Cancer cells accumulate genetic changes that influence the development of cancer. These changes can also influence the response to treatment. Genetic analysis can be done on the tumour (tissue obtained by biopsy or surgery) to identify treatment options.
Breast cancer example: a mutation of the HER2 gene in cancer cells promotes tumour growth. Following the biopsy, this gene or its protein is tested and when positive, the person is eligible to receive treatment targeting HER2 (e.g., trastuzumab (Herceptin) or pertuzumab (Perjeta))
- There is no targeted therapy available for all types of genetic variants;
- Some changes can be identified in genes known to be associated with hereditary predispositions, the BRCA1 and BRCA2 genes being examples. The analysis of the tumour makes it possible to identify the presence of the genetic variation but does not make it possible to determine whether it is an acquired variation (only present in the tumour) or hereditary (in all cells and therefore transmitted from one generation to the next).
Using the same type of technology as non-invasive prenatal screening, a liquid biopsy is a test that measures the DNA levels of a tumour or the level of tumour cells circulating in the blood. The liquid biopsy is being studied to help predict recurrence, survival and predicting response to treatment in people with cancer.
- The type of test performed varies from test to test, and some tests detect fewer genetic variants. So a “negative” result with a limited test could be positive with a more complete analysis;
- Currently, a liquid biopsy is not useful for all types of cancer.
The Place of Genetic Counselling in Precision Medicine
A genetic counselor can help you determine whether or not a genetic test is relevant for your situation. They can also explain the advantages and limitations of a test to help you make an informed decision.
Because genetic tests tell you information about your DNA, which is shared with other members of your family, sometimes a genetic test result can affect other members of your family. For example, in the situation where a genetic test on a tumour identifies a variation in a gene associated with hereditary cancer, a genetic counselor can help you understand the possible impacts, organize tests to confirm if it is hereditary predisposition or not and explain the results. In addition, if a hereditary predisposition is confirmed, the genetic counselor can offer you support and resources to help you communicate this information to your family.
Genetic counselors are used to working in a field that is always changing and expanding and are available to help you use and understand these new options.
Nathalie Bolduc, MSc, CGAC, CGC
Certified genetic counselor