BRCA1 and Hereditary breast and ovarian cancer syndrome: We initially sequenced the corresponding genomic coding region, comprising all exons and exon–intron boundaries, in blood DNA samples from 300 Spanish breast cancer index cases that fulfilled one of the criteria suggestive of hereditary breast and ovarian cancer (HBOC) syndrome, but were negative for pathogenic mutations in BRCA1 or BRCA2 genes (see Methods).