BRCA1 is a large gene, located on the 17th chromosome and this gene has a very complex three dimensional structure and function. Mutations on the BRCA1 gene can occur in several parts of the large gene and till now about 500 or more different kinds of mutations are identified on BRCA1. Siblings inherit BRCA1 mutations as an autosomal dominant pattern, which means the features of the mutated gene can be expressed just with the passing of single copy of the mutated gene from any one of the parents.

BRCA1 mutations are associated with increased risk of breast malignancy during the life of the person possessing the mutated gene. A woman carrying BRCA1 mutation has about 56 to 85 % chance of developing a breast cancer diagnosis in her lifespan. Apart from the risk of development of breast malignancy, BRCA1 mutations are also associated with higher risk levels of ovary cancers and prostate cancers in the carrier of the mutated gene. The association of BRCA1 mutation and ovary cancer is very much marked and a woman carrying BRCA1 mutation has aproximately 15 % to 45 % risk of having ovary cancer in her lifetime. By comparison only about 1.8 percent of women with no inherited BRCA abnormality get a diagnosis of ovary cancer. The association between prostate cancer and male carriers of BRCA1 is not as good compared to breast cancer and ovary cancer risk, seen in women, but evidence shows there is a close link between the two entities.

BRCA2.
BRCA2 is a large gene located on the 13th chromosome. BRCA2 is about twice the size of BRCA1 gene and has a complex structure and function. In contrast to to BRCA1, male carriers of BRCA2 gene have an increased chance of development of breast cancer. The incidence of male breast cancer is very small and is aproximately 1 in 100 of the of breast cancer rates in women. Hence all male patients with breast cancer should be evaluated for BRCA2 gene mutations, particularly if they were found to have other first degree relatives who had a diagnosis of breast cancer in the past. BRCA2 carrier men have about 6 percent risk of breast cancer development in his lifetime. In contrast to BRCA2, men who carry BRCA1 do not have any significantly elevated risk in breast cancer development. Mutations in the BRCA2 gene are also associated with increased risk of ovarian cancer, pancreas cancer and cancerous melanoma. Together BRCA1 and BRCA2 account for the most of the genetic breast cancers.

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