...mutations in some genes cause a disease that is already present and obvious at birth, while other mutations do not directly cause the disease but can increase the likelihood that you will develop it later in life? Breast cancer is the most common cancer in women and the second leading cause of death, with its incidence steadily increasing worldwide. About 10-15% of cases are associated with a clustered occurrence in a particular family, so there is a direct link to heredity. Several studies have confirmed that mutations in the BRCA1 and BRCA2 genes are directly involved in the development of breast cancer. The product of the BRCA1 gene is a protein that suppresses tumour formation by participating in the repair of damaged DNA, when mutated this checkpoint does not occur and the cells undergo rapid replication with lots of DNA errors. A woman diagnosed with breast cancer should therefore always undergo a genetic examination to check if she has the BRCA1/2 mutations. If she has already succumbed to the disease, her closest female relatives should also go for a genetic examination. Mutations in these genes are considered genetic "markers" that indicate a woman's lifetime risk of developing cancer. While screening can reveal a genetic predisposition, a positive test result does not mean that an individual will absolutely develop the disease, but the risk is much higher. However, it is important that the carrier of such a mutation be under increased medical supervision.