Epidemiological

Epidemiological studies suggest that mutations in BRCA1
account for 2% of all breast cancers and, at most, 5% of
ovarian cancer. Mutations in BRCA2 account for less than
2% of breast cancer in women, 10% of breast cancer in men
and 1% of ovarian cancer. Most clustering of breast cancer
in families is therefore probably due to the influence of
other, as yet unidentified, genes of lower penetrance,
with or without an effect from modifying environmental
factors.