Genetic

Genetic tests for breast cancer prevention and treatment are now implemented in most modern medical facilities. A recent review highlights the role of genetic testing in this context and describes when, why and how it should be performed.

 

Breast cancer ranks among the top most frequent cancers in the U.S. affecting one out of 800 women. A significant proportion of these cancers arise from inherited mutations that dramatically increase the risk of developing breast cancer as well as other cancer types. Among the most frequent mutations underlying these inherited cases are those affecting two genes known as BRCA1 and BRCA2, which are responsible for 30% of all inherited breast cancer cases. Both encode proteins having roughly similar biological functions in protecting our genome from deleterious mutations that may drive cancer progression or initiation. In addition, other less frequent mutations, including TP53 and PTEN mutations, may underlie some inherited breast cancer cases. However, the clinical syndromes associated with these latter mutations include an increased risk for many other cancer types. Therefore, unlike BRCA1/2, TP53 and PTEN mutations do not specifically drive breast cancer and rather influence tumor development across a wider variety of tissues.

The predisposition associated with these breast cancers can be genetically detected using a standard genetic test. In fact, this information may be instrumental as a positive test means implementing risk-reducing strategies such as increased surveillance, preventive chemotherapy or even mastectomy. However, these tests should be performed only in specific cases for medical, psychological and economic reasons. Thus, in order to help general surgeons determining which cases warrant genetic testing, a recent review published in JAMA Surgery thoroughly reported commonly accepted guidelines for the use of genetic tests.

The authors first start by discussing when to go forward with BRCA1/2 preventive genetic screening tests. According to many medical advisory committees, it is generally acknowledged that a personal family history of BRCA1/2 mutations, early-onset (<50 years of age) breast cancer, two or more primary breast cancers and Ashkenazi Jewish heritage argue in favour of using genetic tests. Although the test itself may seem harmless, it only appears to benefit patients at high risk of breast cancer while patients at lower risk have essentially no or even negative impacts. Notably, these tests may also be particularly useful for women who have already been diagnosed with breast cancer as it can guide the physician in choosing the best treatment strategy. In this scenario, the criteria for performing the test include early disease onset, two or more primary breast cancers, triple-negative breast cancers (which are particularly aggressive), close relatives with early-onset breast cancer and a family history of ovarian cancer.

The method underlying these genetic tests is based on the PCR amplification of a BRCA gene segment followed by forward and reverse sanger sequencing of the amplicon. The test is more commonly known as BRCAnalysis and it has been the gold standard of most medical facilities until 2013. However, this method suffers from limitations inherent to the fact that some categories of mutations will always remain undetected, although the error rate is still relatively low at 1%. Moreover, patients testing negative for the BRCA1/2 test despite the presence of evidence supporting the existence of a hereditary component may be considered for testing other genes such as PTEN and TP53. The authors finally discuss the additional contribution of genetic counseling when considering genetic tests. Genetic counselors typically accompany patients in interpreting the results of the genetic tests, advising about prevention strategies and dealing with many other related psychological aspects. The benefits of genetic counseling include decreased risk perception, decreased intention for testing among low-risk patients and decreased anxiety. In summary, when performed under the right circumstances and with the appropriate medical and psychological assistance for the patient, these tests have the ability to save patients lives and this review provides physicians with clear guidelines to reach this goal.

 

Written By: Samuel Rochette M.Sc

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