Genetic Basis (Genes involved)
According to the American Cancer Society Breast cancer is a tumor that starts in the cells of the breast tumor is a group of cancer cells that grow into (take) surrounding tissues or continue to spread to the other areas of the body. This disease occurs almost entirely in women, but men can get it, too. Many factors increase the chance of developing breast cancer, but it is not known exactly how some of these risk factors cause cells to become cancerous. Hormones seem to be one reason in many cases of breast cancer but it’s not understood why yet. Inheritable genes are of the many also.
Certain inherited DNA mutations increase the risk of developing certain cancers and are responsible for the cancers that run in families. In example, the BRCA genes (BRCA1 and BRCA2) are tumor suppressor genes. A mutation in one of these genes could be inherited from a parent. When one of these genes are mutated, it no longer suppresses abnormal growth, and cancer is more likely to develop. Mutations in tumor suppressor genes like the BRCA genes are considered “high-penetrance” because they often lead to cancer. It is said that many of the women with high-penetrance mutations develop cancer, most cases of cancer (including breast cancer) are not caused by this kind of mutation. More often, low-penetrance mutations or gene variations are a factor in cancer development. Each of these may have a small individual effect on cancer development, but the overall effect on the population can be large because they are common, and people often are affected with more than one at the same time. The genes involved may affect things like hormone levels, metabolism or other things that interact with risk factors for breast cancer. These genes may be responsible for much of the risk of breast cancer that runs in families.
Most DNA mutations related to breast cancer occur in single breast cells during a woman's life rather than being inherited. These acquired mutations of oncogenes and tumor suppressor genes may come from other factors like radiation or cancer-causing chemicals. So far, the causes of most mutations that could possibly lead to breast cancer are still unknown. Most breast cancers have several acquired gene mutations. While it has long been recognized that a proportion of breast cancer cases are the result of an inherited familial predisposition, precise knowledge of the underlying genetic processes has been lacking. Recent advances in molecular biology, however, have shown that hereditary breast cancer may eventuate as a result of mutations on several specific gene loci including BRCA1, BRCA2, ATM gene, PTEN and p53. Several other less frequently occurring predisposition genes such as the androgen receptor gene (AR), the HNPCC genes and the estrogen receptor gene may also be involved, but to a lesser extent. Overall, approximately five to ten percent of all breast cancers are thought to involve one of these inherited predisposition genes, with BRCA1 and BRCA2 being responsible for as much as 90% of this group. Because of the complex nature of genetic testing, mutation analysis is not presently routinely available outside genetic counselling clinics.
Breast cancer is not just one disease. It is a complex group of diseases that occurs in an environmentally complex world. We are exposed to multiple chemicals and radiation sources in the course of our daily lives. Environmental factors may include things found in nature that we eat, drink, touch or breathe, as well as man-made factors. Possible examples