Friday 26 May 2017

Hereditary Cancer and Genetic Testing: 1 Size Does Not Fit All

By Sarah O'Sullivan, Genetic Counsellor

The Role of Genetic Counselling and Testing 

Genetic counselling and genetic testing can provide information that is life-saving – a person who did not know they carry a cancer predisposition gene fault can gain this knowledge and more importantly, the opportunity to implement effective risk reduction strategies.

In 2013, a light was shone on this important area of preventative healthcare by Angelina Jolie, who shared her personal experience of cancer genetics – testing had shown that she carries a BRCA1 gene fault, which causes Hereditary Breast/Ovarian Cancer (HBOC), and at the time she was undertaking preventative surgery to minimise her risk of breast cancer.

In the space of one New York Times opinion piece, increased awareness of cancer genetics was achieved in a way that had not been seen before.

While this outcome was overwhelmingly positive, for some people – patients and healthcare providers alike – a perception was created that there is a single genetic test that provides conclusive results about cancer risks and risk management options.

In practice, cancer genetics is rarely straight forward, and genetic counselling can help to simplify the pathway.

There are many genetic tests that can provide much useful information, but these tests also have the potential to raise more questions than are answered.

The Important Factors to Consider in Cancer Genetics

There is no 'one size fits all' cancer genetics test, and an individualised approach to the potential advantages and limitations of genetic testing is essential.

For every patient who considers genetic testing for hereditary cancer, there are many factors to consider before testing proceeds:

What is the patient's personal and family history of cancer?

  • Are they suggestive of a cancer predisposition syndrome that warrants testing of one or two genes only? Or would testing a broader panel of genes be more informative?
  • Could the patient be reassured that he/she is at general population risk of cancer? 

Has genetic testing been undertaken in another family member? 

  • If so, what is the result and what are its implications for the patient?

Who is the ideal candidate for testing in the family?

  • Would testing of another family member be more informative for the patient and other at-risk relatives?

What is the clinical utility of genetic testing for the patient?

  • Will the result change the patient’s risk assessment, risk management options or health behaviour?

What is the patient's experience with cancer and genetic testing? 

  • How do the patient’s experiences influence their perception of risks, testing and results?

What are the psychosocial factors to consider? 

  • Genetic testing can have a wide range of non-medical implications, including emotional, financial and reproductive.

Is this the appropriate time for testing to be undertaken?

  • For some patients, delayed testing may be worth considering in some situations, such as during pregnancy or during cancer treatment.

Exploration of these factors helps to guide whether genetic testing is appropriate for the patient and if so, which is the best test to be undertaken. 

For some patients, the outcome of genetic counselling is that genetic testing does not go ahead – they may be reassured that their cancer risks are equal to those of the general population, or they may not change their health behaviour regardless of the result. 

Others will decide to undergo testing to clarify their cancer risks, and those of other family members. 

Understanding The Limitations and Implications of Genetic Tests 

Given the ever-increasing array of genetic tests that are available, choosing the most appropriate test for the patient is critical, as is helping the patient to understand the benefits, limitations and implications of their results.

Testing may be requested for a small number of genes that have a lot of data and experience behind them, such as the BRCA1 and BRCA2 genes that are associated with HBOC. 

If a gene fault is identified, then a wealth of information and options are available to help the patient maximise the benefits of knowing their genetic status. 

In contrast, technological advances have recently enabled the cost-effective testing of numerous genes that are associated with hereditary cancers. For many genes included in these larger gene panels, clinically useful information is currently limited. 

Therefore, if testing identifies a fault in one of these genes, the patient may be left in the position of knowing that they carry a gene fault, but not knowing what the associated risks are, or how to manage them; in turn, the patient’s family members may find themselves in the same position. 

For some patients, this uncertainty can raise anxiety and the question of whether testing should have been undertaken in the first place; for others, the uncertainty is well-tolerated and viewed as information that may be of use in the future – one size does not fit all.

The Gene Variant of Uncertain Significance (VUS) 

Testing of more genes also increases the likelihood of identifying a gene variant of uncertain significance (VUS). 

Most genetic variation between individuals is benign, and does not cause any health problems; rarely, genetic variation stops the gene from functioning and this may be associated with disease – cancer in the case of cancer predisposition genes. 

When a VUS is identified, the result cannot be interpreted as insufficient information is available to know whether the variant is benign or associated with disease. 

A VUS can be a source of confusion, anxiety and frustration for the patient and their family members, and requires careful management. 

Some genetic testing and results should be considered as dynamic, and likely to change with time and additional information. 

Bigger is Not Always Better 

While the availability of large gene panels is a promising advance for cancer genetic counselling, bigger is not always better.

Much has changed in the field of hereditary cancer in recent years – knowledge has increased, technology has improved and awareness has broadened. 

This upward trajectory is expected to continue into the foreseeable future, bringing with it both increased options and increased complexities. 

Many patients arrive at the cancer genetic clinic saying, “I just want to have the gene test for cancer”, and leave with a much better understanding of the various testing options and their implications, having made an informed decision about the best way forward for them. 

Cancer genetics is usually not just a matter of having a test, and for now, genetic counselling plays an essential role in helping patients to navigate their way through evolving genetic territory. 

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IMPORTANT: The information on this blog is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment in any manner. Always seek the advice of your doctor or other qualified health provider with any questions you may have concerning your health or anything related to it. 

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