Among 113 Japanese breast cancer families, we have identified 15(13 %)and 21(19 %)deleterious germline mutations in
BRCA1 and
BRCA2 genes, respectively. Among patients with
BRCA1 or
BRCA2 mutation carrier, breast cancers occurred in significantly younger women with higher frequency of bilateral breast cancers as compared with non-carriers. The estimated cumulative lifetime risk of breast cancer for women who carry
BRCA1 or
BRCA2 mutations was nearly 80%. In BRCA1 breast cancers, a higher rate of histological grade III and a higher frequency of estrogen-receptor negativity were characterized as compared to sporadic cancers. On the contrary, there was no significant difference in cancers between
BRCA2 mutation carriers and non-carriers. These clinicopathological factors found in Japanese
BRCA1 or
BRCA2 mutation carriers seem to be similar with those of Caucasian mutation carriers.
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