When we read about genetic testing in the mainstream media, we often think of the testing Angelina Jolie had, called germline genetic testing. This analysis looks for genetic changes in our DNA that are found in most of the cells in our body, including cells in the blood, saliva, and cheek cells, which are generally the samples tested. DNA is inherited from our biological parents -50% from our mothers and 50% from our fathers. Genetic changes found in our DNA are often inherited from one or both parents and can be passed on to children.
Another type of genetic testing has gained popularity over the past decade, and that is somatic or tumor testing. All tumors have genetic changes that cause the cells within the tumor to grow under its own control and ignore many of the natural checks of a normal cell. Genetic testing on a tumor sample involves gathering cells from a tumor, usually by biopsy or surgical removal, and performing genetic testing on those tumor cells. This testing can lead to better understanding of the tumor and which therapy would be most effective. Mutations found in a tumor often arise only in that tumor, and not in the other cells of a person’s body. This testing is also called precision medicine or personalized medicine. Many companies, including Foundation Medicine, focus on somatic testing.
Somatic mutations are usually not inherited – but sometimes they can be inherited. In fact, the NCCN guidelines recently changed to include people who have a BRCA mutation detected in their tumor as candidates for germline testing. This additional testing will help determine if they also carry that BRCA mutation in the rest of the cells of their body*.
If a person does carry a germline mutation in BRCA:
- he/she is at risk for the other BRCA-related cancers, and
- can pass this mutation on to children
If a person does not carry a germline mutation in BRCA:
- this mutation is most likely present only in the tumor.
Germline testing would, therefore, be important to determine whether other family members are at increased risk to develop cancer, to make informed decisions about medical management, surgical- and radiation-decision making, and also to reduce the risk of developing another BRCA-related cancer. Such testing is important to both men and women.
Keep in mind that BRCA mutations can be found in all types of tumors – including those outside the spectrum of BRCA cancers. A person diagnosed with lung cancer, for example, could be found to carry dozens of mutations in that tumor, including a BRCA mutation. That finding could then lead to germline testing.
Also keep in mind that there are hundreds of genes involved in tumor genetics, and BRCA1 and BRCA2 are only two of them.
In summary, as we learn more about precision medicine and somatic genetics, we will likely learn of more and more areas of crossover that may require genetic counseling and germline testing.