Familial breast cancer

Breast cancer is the commonest cancer seen in young women
from developed countries, affecting about 20% of all women
who die of cancer. Although the majority of breast cancer cases
are sporadic, approximately 5% have an inherited component.
The two susceptibility genes identified so far are BRCA1 and
BRCA2. The BRCA1 gene on chromosome 17q21 is involved in
45–50% of inherited breast-only cancer and 75–80% of
inherited breast/ovarian cancer. The BRCA2 gene on
chromosome 13q12-13 is involved in approximately 35% of
inherited breast-only cancer and 20% of breast/ovarian cancer.
In addition, BRCA2 is involved in a significant proportion of
male breast cancer.