Cancer Genetics
Is Cancer Genetic?
All cancer is genetic in one sense: Cancer means that cells in the body have acquired mutations and are growing out of control.
Is Cancer Inherited?
Although cancer itself is never inherited, genetic factors that increase susceptibility to developing cancer may be inherited. Most cancer, however, is considered “sporadic”—not familial or hereditary. Age, environmental factors, and random chance all contribute to the development of sporadic cancer. When cancer is diagnosed at younger ages than is typical or when there are multiple cancer diagnoses in a family that fit a certain pattern, it can be reasonable to consider the possibility of an inherited susceptibility to developing one or more specific types of cancer.
Why does my family history matter? Doesn’t it make more sense just to get tested?
Both inherited genetic and environmental factors may contribute to the risk of developing cancer. Environmental factors are often shared within families. Familial genetic risk factors may be spread out over hundreds of genes. The risk conferred by these genes individually may be minor. Taken together, however, the risk conferred may be significant. Risk conferred by a number of different genes is often best appreciated when looking at a family history of cancer rather than actually analyzing genes. This is one reason why knowing your family history of cancer and sharing the information with your healthcare provider can be important in guiding your personalized plan of care—even in the absence of genetic test results, and even or especially when genetic test results are negative.
Hereditary Cancer Syndromes
In a minority of cancer cases, a mutation in one specific gene may be identified that confers a high risk of developing one or more specific types of cancer. This mutation in a single gene often helps to explain atypical patterns of cancer that have been seen in an individual or in a family. When significantly increased cancer risks are associated with a mutation in a single gene, the term ‘hereditary cancer syndrome’ is often used.
A positive genetic test result in a gene associated with a recognized hereditary cancer syndrome provides valuable information about an individual’s cancer risks and can be extremely helpful in guiding an individual’s personalized plan of care.
What is the Impact of Positive Results on a Personalized Plan of Care?
- Different or increased screenings may be recommended. Sometimes, as in the case of colonoscopies, these increased screenings can significantly reduce the chance of developing cancer. In other cases, as with mammograms and breast MRIs, screening can significantly increase the likelihood of early detection, prompt treatment, and good outcomes.
- In some cases, preventative surgeries may be considered to reduce to close to zero the chance of developing a cancer for which an individual would otherwise be at a very high risk.
While there are many different hereditary cancer syndromes, most of them are rare. Only two hereditary cancer syndromes are relatively common in the general population.
What are the Two Most Common Hereditary Cancer Syndromes?
Breast & Ovarian Cancer
Cancer Risks and the BRCA Genes
Hereditary breast and ovarian cancer is associated with mutations in the BRCA1 and BRCA2 genes. Mutations in either of these two genes confer a significantly increased risk of developing breast and ovarian cancer as well as a more modest increase in risks for developing pancreatic, prostate, and skin cancer.
About 1/200 – 1/500 individuals in the general population carry a mutation in one of these two genes. If you have a significant personal or family history of breast and/or ovarian cancer, however, your chance of carrying a mutation in one of these two genes would be higher than this general population risk and testing of these genes may be reasonable.
Beyond BRCA
Within the past few years, clinical testing of other genes associated with a significantly increased risk of breast and/or ovarian cancer has become available. If you previously had genetic testing of the BRCA genes done and had a negative test result, it would be reasonable to consider additional testing of other genes associated with breast and ovarian cancer.
Although individuals who have breasts and ovaries are most likely to develop BRCA-related cancer, individuals who do not have breasts or ovaries are just as likely to have BRCA mutations.
Hereditary breast and ovarian syndrome received a lot of public attention when Angelina Jolie spoke out about her family history of cancer, her decision to have genetic testing done, and the preventative surgeries she had after learning that she did carry a mutation in the BRCA1 gene.
Lynch Syndrome
Although Lynch syndrome receives much less public attention than Hereditary breast and ovarian cancer, it is just as common, affecting 1/200 – 1/500 individuals in the general population.
Lynch syndrome is caused by mutations in any one of several different genes (MLH1, MSH2, MSH6, PMS2, EPCAM). Individuals with Lynch syndrome have high risks of developing colon and uterine cancers, significantly increased risks for stomach and ovarian cancer, and more modestly increased risks for a number of other cancers.
Although the uterine and ovarian cancer risks only apply to individuals who have these gynecologic organs, individuals without these organs are just as likely to have Lynch syndrome.
These are some instances in which genetic testing for Lynch syndrome should be considered:
- colon or uterine cancer diagnosed < 50yo — or even < 64yo
- colon cancer diagnosed at any age with specific features found on pathology testing
- 3 or more diagnoses in a family of cancers associated with Lynch syndrome (colon, uterine, ovarian, stomach), especially if the diagnoses occur in two different generations.
What is my individualized risk assessment?
Cancer genetic counseling takes these general genetics principles and applies them to your specific family medical history and unique concerns as an individual. A cancer genetic consultation involves review of 3-4 generations of your family medical history, with a focus on cancer diagnoses. Discussion includes the likelihood that the cancers in your family have a hereditary contribution; if and how genetic testing may help to clarify these risks; and differences in genetic testing options, including analytical and interpretive differences between different genetic testing products.
If, after counseling, you are interested in moving forward with genetic testing, we will work with your chosen healthcare provider to order testing and be available to them for any questions they may have about test results and implications for your personalized plan of care. If you have already had cancer genetic testing done, we will discuss these results with you as well as if and why further genetic testing may be recommended for you.
Do you have more questions?
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