BRCA1 and cancer: The observed BRCA1 to BRCA2 case ratio of 1.0:1.8 is consistent with ratios in other relevant work.29,30,31 Previous research3 shows decreased penetrance for BRCA2 carriers, which may be a contributing factor in the underascertainment of these cases compared with BRCA1 cases; in our study, among those with prior testing and cancer diagnosis, more than 90% had BRCA1-associated cancer risk.