Decreased BRCA1 and USP4 was observed in 59% (134 of 226) and 63% (143 of 226) of breast cancer respectively, whereas only 10% (23 of 226) and 8% (18 of 226) exhibited high expression (Table 1), suggesting that both BRCA1 and USP4 are downregulated in human breast cancers. Here, BRCA1 is linked to breast cancer.