Genetic Counseling and Testing
The vast majority of cancers, about 70-85%, are sporadic. This means that they happen due to random chance, bad luck, or environmental factors (such as smoking causing lung cancer, or sunlight causing skin cancer). Using genetic testing, physicians try to find out if the cancer is hereditary, meaning it can run in families. Only about 5-10% of all cancers are hereditary, so this is quite rare. We can do genetic testing, which is a blood test, to determine if a person has a hereditary predisposition to developing certain types of cancers.
- Role of Genes
- Common Misconceptions
- About Genetic Counseling & Testing
- Common Hereditary Cancer Types
All cancer is caused by changes in our genes, but not all cancer is hereditary. Genes are pieces of DNA, and each gene has a specific job in our bodies. For example, we have genes that control eye color, hair color, and height. Additionally, we have other genes that protect us from developing cancer. When these genes have a mutation (a change in the DNA), they can no longer do their job properly and cannot protect us against developing cancer as well as they did before. As a result, cancer is more likely to occur, but it is not guaranteed.
Everyone gets two copies of each gene: one from mom and one from dad. People with hereditary cancer syndromes were born with a mutation in one of these copies, so the mutation is in every cell of their bodies. However, people with sporadic cancer were not born with a mutation. The purpose of genetic testing is to determine if a person has a hereditary cancer syndrome by seeing if they have a genetic mutation in every cell of the body, including their blood. This is determined by doing a blood test. A person with a hereditary cancer syndrome has an increased chance to develop certain cancers, depending on which gene has a mutation.
Additionally, if a person has a genetic mutation in every cell of their bodies, this means it will be in their sperm or eggs as well. Therefore, people who have hereditary cancer mutations have a 50% chance of passing the mutation along to each of their children. As a result, these children may also be at an increased risk to develop cancer throughout their lifetimes.
A common misconception is that cancer “skips generations,” but this is not true. Mutations in cancer genes increase the risk of developing cancer, but cancer is not guaranteed to occur. As a result, some people in the family may develop cancer, while others may not, even if they have the genetic mutation.
Another misconception is that hereditary cancers can only affect women, but this is not true either. Hereditary cancer syndromes can affect both men and women. Some hereditary cancer syndromes increase the risk of cancers that are more likely to occur in women, but men can also carry the mutation and can pass it on to their children. As a result, both men and women are offered genetic counseling and genetic testing for hereditary cancers.
Genetic counselors are healthcare providers who have Masters Degrees in Genetic Counseling. They are trained in genetics, education, and psychology in order to provide the best care for their patients’ needs. Genetic counselors examine each patient’s personal medical history, as well as the family history, to determine if any red flags point to a hereditary cancer syndrome. Genetic counselors can perform risk assessments and order genetic testing for their patients.
Genetic testing for hereditary cancer is a blood test that looks for mutations in certain genes. About 45 genes are known to be linked to increasing the risk for different cancers. However, most people do not need to be tested for all 45 of these genes. A physician or genetic counselor will determine which genes are appropriate to test, based on each patient’s personal history and family history.
After having a thorough discussion with your physician or a genetic counselor, you can decide if you would like to pursue genetic testing and how much information you would like to know. Genetic testing may be recommended in some cases, but it is never required. Genetic counselors are able to educate, answer questions, alleviate concerns, and help guide you through the decision-making process.
If you are found to have a genetic mutation, we can then test your family members to see if they have the same genetic mutation as you do. If they do, we offer them increased screening and management options. However, if they do not have the mutation, they are probably not at increased risk of developing cancer. Therefore, they should continue the same screening that is recommended for the general population.
Some people who have the following types of cancers running in their families may have a hereditary predisposition (or increased chance) to develop these cancers. The types of associated cancers and the percentages for developing each cancer over a lifetime depends on which gene has a mutation.
Breast and Ovarian Cancer
Breast cancer is quite common, as 1 in 8 women in the general population will develop breast cancer in their lifetimes. However, only about 5-10% of all breast cancers are hereditary. Ovarian cancer is rarer, as about 1 in 75 women in the general population will develop ovarian cancer in their lifetimes. However, up to 24% of ovarian cancers are hereditary. Therefore, ovarian cancer is rarer than breast cancer, but it is also more likely to have a hereditary component.
About 25 genes are known to increase the risk of developing breast and ovarian cancer. Some of these genes greatly increase the risk of developing these cancers, while other genes moderately increase or slightly increase the risk. The most well-known genes associated with breast and ovarian cancer are BRCA1 and BRCA2, and these are considered high-risk genes. Mutations in BRCA1 and BRCA2 cause BRCA-associated Hereditary Breast and Ovarian Cancer (HBOC). A woman who has a mutation in either of these genes has up to an 85% chance of developing breast cancer over her lifetime and up to a 55% chance of developing ovarian cancer over her lifetime. The BRCA1 and BRCA2 genes are also associated with an increased risk of developing other cancers, such as prostate cancer, pancreatic cancer, male breast cancer, and melanoma.
Scientists know a lot about BRCA1 and BRCA2, so we know how to take care of people who have mutations in these genes. Experts in cancer genetics have created guidelines on what screening and management steps to take for people with BRCA1 and BRCA2 mutations. We often recommend increased screening, such as more frequent mammograms and breast MRIs to try to catch breast cancer early when it is most treatable. Sometimes, prophylactic surgeries are available for those who are interested, such as removing the breasts or ovaries before cancer develops.
Other genes are known to be associated with breast and ovarian cancer. However, these other genes may not increase the risk of cancer as much, or scientists may not know as much about them yet. Genetics is a growing field, so we are still learning a lot about cancer genes every day. For these moderate-risk genes or newly identified genes, we determine screening and management recommendations for each patient on a case-by-case basis.
Colon cancer is also quite common in the general population, as about 1 in 21 men and 1 in 23 women will develop colon cancer in their lifetimes. However, we do know that mutations in certain genes increase the chance of a person developing colon cancer along with other cancers.
Mutations in one of five mismatch repair genes are known to cause Lynch syndrome (otherwise known as Hereditary Nonpolyposis Colorectal Cancer, or HNPCC). Lynch syndrome is associated with less than 10 colon polyps. These polyps are typically not cancerous, but they can turn into cancer if they are not removed. People with Lynch syndrome have about a 70% chance of developing colon cancer if they do not get their polyps removed. Lynch syndrome is also associated with an increased chance of developing uterine cancer (also known as endometrial cancer), ovarian cancer, other GI cancers, and possibly some other cancers. Guidelines recommend more frequent colonoscopies to identify and remove colon polyps for those with Lynch syndrome. Similarly, prophylactic surgeries to remove the uterus and ovaries before cancer develops are available options to those who are interested.
Another hereditary colon cancer syndrome is known as Familial Adenomatous Polyposis (FAP). FAP is caused by mutations in the APC gene. People with FAP will develop 100 or more colon polyps in their lifetimes. Again, these polyps are typically not cancerous, but they can turn into cancer if they are not removed. People with FAP have about a 100% chance of developing colon cancer if the polyps are not removed. However, because so many polyps exist, guidelines recommend that the colon itself must be removed. FAP is also associated with an increased chance of developing thyroid cancer, small intestine cancer, other GI cancers, and possibly some other cancers. Increased screening guidelines exist for some of these cancer types.
Other Hereditary Cancer Syndromes
- Li-Fraumeni syndrome (LFS) Associated with breast cancer, brain cancer, leukemia (blood cancer), sarcomas (cancer of the bone or muscle), adrenal gland tumors, and possibly many other cancers
- von Hippel-Lindau syndrome (VHL) Associated with kidney cysts or cancer, hemangioblastomas (overgrowth of blood vessels), pancreatic cysts or cancer, and pheochromocytomas (a type of adrenal gland tumor)
- Multiple Endocrine Neoplasia, Type I (MEN1) Associated with hormone-secreting tumors: parathyroid gland tumors, pituitary gland tumors, pancreatic tumors, and other GI tumors
- Multiple Endocrine Neoplasia, Type II (MEN2) Associated with medullary thyroid cancer, pheochromocytomas (a type of adrenal gland tumor), parathyroid gland adenomas, and other GI tumors
- Neurofibromatosis, Type I (NF1) Associated with café-au-lait spots (flat coffee-colored birthmarks), freckles in the armpit and groin areas, neurofibromas (tumor formed by a nerve cell), spots and tumors in the eye, and sometimes learning disabilities
Do you have questions about cancer genetics or concerns about your personal or family history? Email firstname.lastname@example.org or ask your healthcare provider.