ABCG2 and breast cancer: For example, a combination of erlotinib and olaparib that covers four SL pairs, including ABCG2 + BRCA1, BRCA1 + EGFR, BRCA1 + PARP1, and BRCA1 + PARP2, which may have a potentially enhanced therapeutic effects with reduced resistance for hereditary breast cancer and ovarian cancer with the BRCA1 mutation28.