Genes and Cancer
We are all born with two copies of approximately 25000 genes that are present in all almost all cells of the body. Every time a cell divides this large volume of genetic information is copied into the daughter cells. This process is prone to errors which lead to DNA damage or mutations. Cancerous cells are often cells that have accumulated several such mutations over a period of time and have acquired the ability to grow and spread uncontrollably. So all cancers are “genetic” however not all cancers are “hereditary”.
Hereditary Breast Cancer
About 5-10 percent of all breast cancers are caused by known inherited abnormalities or mutations in specific genes.
80-90% of hereditary breast cancer is caused by mutations in BRCA1 or BRCA2 gene. BRCA genes normally repair DNA strand breakages that occur during cell division. When a BRCA gene is defective, it fails to repair these errors, leading to development of cancer. The inheritance is ‘autosomal dominant’ meaning that only one copy of the defective gene is sufficient to develop the syndrome. A defective gene copy can be inherited from the father of mother and rarely may develop “de novo” or without being present in the parents.
TP53, PTEN,CDH1, ATM, CHEK2 and PALB2 are other genes responsible for hereditary cancers. Up to 20 percent cases may be familial, i.e. multiple family members may have history of cancer even if no mutations are known or found.
Suspicion of Genetic causes
The possibility of a genetic mutation is suspected in scenarios such as
Young Breast cancer: Breast Cancer is diagnosed at or before age 50 years
Bilateral Breast Cancer: Breast Cancer is present in Both Breasts
Ovarian cancer: of epithelial origin.
Multiple breast cancers: either developing at one time or sequentially
Male breast cancer: At any age
Triple-negative type of breast cancer, particularly in a woman at age < 60 years.
Breast cancer in a patient who has a close relative having breast, ovarian, pancreatic, or high grade prostate cancer.
A previously identified BRCA1 or BRCA2 gene mutation in the family
Breast cancer in ethnicities where the mutation is common (e.g.Ashkenazi Jewish ancestry)
The Genetic Testing Process
Genetic testing is a multi-step process that involves
A)Pre-test Genetic Counseling: You should always undergo a detailed and thorough session of genetic counselling prior to undergoing a genetic test. A genetic counselor or an oncologist with experience in genetics should ask you about your cancer history, the composition of your family tree, known cancers in the family. We may need to verify some pathology reports and do a physical exam with some measurements when needed. The benefits of testing and any possible downside will be explained to you. It is important that you understand what options are available to you if you were to have a positive, negative or inconclusive result. We may recommend that it is better to test a different family member instead of testing you first. Some patients may need multiple sessions of genetic counselling before proceeding with the actual test.
A simple blood draw provides a good sample for the test.We usually collect 3 ml of blood for the test. A saliva sample can also be used. No biopsy or other procedure needs to be done. The sample is sent to a genetics lab. The genetics lab isolates DNA from the blood and processes the DNA using specialized gene sequencing equipment. A large amount of data is obtained in the process which needs detailed analysis, referencing and then interpretation. A genetic test report is generated, which describes any gene mutations which may be found. The entire process can take 4-6 weeks.
C) Post Test Counseling: You should not try to interpret your own reports as these are written using complex terminology. The An oncologist familiar with breast cancer genetics should guide you at this step. You should take your time to understand what these reports mean. You should use the information you gain about your risk, to make positive health decisions. We can guide you on how to disclose your reports to close blood relatives for their benefit when needed.
Management BRCA mutations
Management of a BRCA positive patient, i.e. a patient with a suspected harmful genetic mutation involves shared decision making between the breast surgeon and the patient. This decision may be influenced by the patients age, details of her family history, whether the patient has completed her family, whether she has already been diagnosed with cancer or other high-risk pathology. The options of management include
Risk reducing surgery :
As BRCA gene increase a woman’s risk of ovarian and fallopian tube cancer. This risk is dramatically reduced by surgical removal of the tubes and ovaries. This procedure is usually advised after a woman has completed her family. This procedure also reduces her risk of future cancer. The most effective way to reduce the high risk of breast cancer however is removal of the breast gland with a bilateral mastectomy. Bilateral mastectomy when performed using nipple-skin sparing technique and immediate reconstruction can be done with excellent cosmetic results
Women who are not yet ready for surgery, can choose to undergo more frequent breast cancer screening. We usually advise 6 monthly visits and typically alternate digital mammography with breast MRI for 6 monthly evaluations. For ovarian cancer screening, a yearly transvaginal /pelvic ultrasound and a blood test for CA-125 levels are typically used. Aggressive surveillance does not decrease risk, but allows early detection of potential cancers that are likely to develop.
Some patients may be prescribed chemoprevention such as tamoxifen. These medications can potentially lower risk but do not prevent all cancers in these patients. As they have certain side effects, they should only be used under guidance from your breast surgeon or oncologist.