Should I get genetic testing?

The best treatment for any disease would be to never get it or to prevent it before it occurs.  This is the basis for the public health policies concerning things such as childhood vaccination.  The discovery of DNA and complex sequencing of genes has brought many new investigative tools to medicine.  The idea of a gene test for cancer is exciting because it conveys the idea that one could get tested to know if they will develop a specific cancer in the future.  With this knowledge in hand one could possibly removing the future site of the cancer before it grows such as removing a gallbladder before gallbladder cancer develops.  The other strategy might be to use this information to screen aggressively for the development of a cancer.  For example, if someone has a genetic test that says they will develop a colon cancer then they could get frequent and early colonoscopies to look for a developing cancer.

While these ideas seem to convey a sense of hope and “magic bullet” approach to treatment of cancer, the reality of this type of testing is much different and far more complex.  Often someone goes to their doctor with the idea, concern or demand for such a test without really knowing how the test is used or what type of information will be conveyed form the test.  The purpose of this article is to explain some of the complexities of genetic cancer testing using breast cancer as a model for discussion.  The discussed points would also apply to many other types of genetic cancer testing.

Some genetic cancer testing tests directly for the DNA of a cancer as it is growing.  For example, a way to screen for the presence of colon cancer includes testing the stool for DNA that might be shed from a colon cancer.  More traditional ways to check for colon cancer are to check for blood in the stool or perform a colonoscopy and look at the surface of the colon for tumors.   Under the best circumstances this type of test will detect about 90% of colon cancers when they are present.  The test performs less well for pre-malignant polyps.  Testing like this is usually much more expensive than simple tests such as fecal occult blood test.

The “cancer gene test” that most people refer to is some type of testing to see if they have a genetic predisposition towards a certain type of cancer or if it will predict growth of a cancer in the future.  There are several problems with this idea.  There are hundreds of genes involved with many different kinds of cancer and it is not possible or practical to test every person for every genetic mutation.  This type of testing is often quite expensive and is not routinely paid for by medical insurance companies without strong evidence that it will benefit the person getting the test.

A genetic test for breast cancer is known as the BRCA gene mutation (there are actually two types BRCA-1 and BRCA-2).  Most women with breast cancer do not have genetic mutations such as BRCA.  Overall about 1 in 8 women will get breast cancer at some point in their life.  A woman with the BRCA mutation has about a 1 in 2 chance of getting breast cancer at some point their life possibly earlier on.  Having this test performed and finding out you carry this mutation does not mean that you have breast cancer.  Having a positive test for this mutation does not mean you will get breast cancer at some point, it just means there is an increased risk.  Is it possible to not have the BRCA mutation and still get breast cancer? Yes, about 90-95% of women with breast cancer do not have a hereditary syndrome such as BRCA.

The results of a test such as BRCA genetic test are not like reading the results of a pregnancy test.  You CANNOT be a “little pregnant.”  You either are pregnant or you are not.  The results of BRCA gene testing are not so black and white.  You may have 80% of the genetic mutation present.  What does this mean?  There is no clear answer for this and how will this information affect your decision making? This is even more unclear.  Is it possible to have a negative BRCA gene mutation test and get a breast cancer from a different genetic mutation? Yes, there are several other gene mutations that can lead to breast cancer such as the PTEN gene.  It is possible for the results of a gene test to be different depending on when they are tested?  Yes, genes can change over time and this may affect the accuracy of a genetic test.

These are just part of the considerations that a physician must consider when ordering genetic testing.  What about psychological impact?  Would it be appropriate to order genetic testing such as the BRCA gene mutation for a child or teenage girl?  What would the knowledge of this test do to her view of life and long term planning?  Is it fair to even give this information to someone so young?  There are some childhood cancers that do require screening and treatment if high risk is considered but routine “screening” for these types of syndromes is inappropriate.  Similarly, the same considerations come into play with adults as well. This is why there are guidelines and suggested rules to help best use this type of testing.  A significant consideration is the cost of this type of testing as well.

Should you ask your doctor to undergo genetic testing?  The best way to deal with this question is to have an open and honest discussion with your doctor to see if you meet any of the recommended criteria for a specific genetic test.  Another key question is what will you do with this information?  This can be a very complex subject and you should carefully consider the implications of a test result before undergoing the test.

REFERENCES:

  1. www.cancer.gov/cancertopics/factsheet/Risk/BRCA
  2. www.ornl.gov/sci/techresources/Human_Genome/medicine/genetest.shtml
  3. Informed consent for BRCA1 and BRCA2 testing.Rimer BK, Sugarman J, Winer E, Bluman LG, Lerman C.Breast Dis. 1998 Apr;10(1-2):99-114. Review.PMID: 15687553
  4. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.