RAD51 and triple-negative breast carcinoma: After long-term treatment with PARP inhibitors, the triple-negative breast cancer cell lines SUM149 and SUM159 had elevated RAD51 expression, further confirming that RAD51 mediates PARP inhibitor resistance; however, knockdown of RAD51 using short hairpin RNA sensitized the cells to the PARP inhibitor olaparib [155].