What are the chances of getting breast cancer?
The majority of all breast cancers are not due to genetic changes in the BRCA genes. Studies have shown that only about 5-10% of all breast cancers are inherited through BRCA mutations. Nevertheless, women whose families have a high incidence of breast cancer are uncertain and wonder how likely they are to get breast cancer.
The probability for women who suffer from a mutation in BRCA 1 or BRCA 2 to develop breast cancer in the course of their further life is about 50-80%, which is significantly increased compared to women with non-mutated BRCA genes. The lifetime risk of ovarian cancer is also increased by changes in the BRCA1 or BRCA2 gene: women with mutations have a 50% chance of developing the disease. Women with mutated BRCA genes also develop the disease significantly earlier at a younger age (40 years or younger).
In women with non-hereditary breast cancer, the disease occurs on average at the age of 60 and later. But mutations in the BRCA genes do not only affect women. Men who are affected by BRCA mutations also have an increased risk of developing breast cancer during their lifetime.
However, these figures only apply to so-called high-risk families, i.e. families in which several cases of breast cancer or ovarian cancer have occurred in family members at an early age. In addition to the two BRCA genes, there are other genes that are believed to increase the risk of hereditary breast cancer. Each gene is duplicated in the cell within the nucleus.
One gene copy comes from the mother, the other from the father. A mutation in one of these copies is sufficient to be called a BRCA mutation, this condition is called a “heterozygous” mutation. This copy of the gene is defective from birth, whereas the second copy is still intact.
If a mutation in the second copy occurs due to environmental influences or spontaneously, the function of the gene fails completely and a “homozygous” mutation is present. As a result, the cell can no longer repair damage in the DNA and grows uncontrollably. Unchecked cell growth leads to tumour formation.
If several cases of breast cancer occur within a family, it is likely that there is an increased susceptibility to the disease and that it is passed on. The inheritance of the BRCA genes follows the scheme of “autosomal dominant inheritance”. This means that a mutation in a BRCA gene is passed on from one parent to the children with a 50% probability. It is important to understand that this is true for all offspring, both female and male, and therefore the mutation can be passed on through men within the family. On the other hand, people who do not have a mutation in the BRCA genes will not pass on BRCA mutations to their children, as gene mutations are only passed on directly to the offspring and cannot skip a generation.
