An interstitial tandem duplication of 9p23-24 coexists with a mutation in the BRCA2 gene in the germ line of three brothers with breast cancer.

Germ-line mutations of the BRCA2 gene account for the majority of families with both male and female breast cancer. However, among independently ascertained families with the same mutation, cases of male breast cancer often appear to cluster in a single family or in a particular branch of one family. This suggests that the risk of male breast cancer conferred by BRCA2 mutations may be modified by other genetic or environmental factors. We report a family in which three brothers with breast cancer carry in their germ line two genetic abnormalities: an insertion A at nucleotide 2041 in exon 10 of BRCA2, which leads to premature termination of the encoded protein at codon 615, and a tandem interstitial duplication involving chromosome bands 9p23-24. We propose that the coexistence of this rare chromosomal abnormality with BRCA2 mutation may be augmenting the risk of male breast cancer conferred by the BRCA2 mutation.