Previous reports have demonstrated that the sensitivity of breast cancer cells to PARPi could be influenced by a combination of factors such as HR deficiency (including BRCA1 status), drug efflux efficiency, activation of 53BP1 pathway, PARP activity,[56] which indicated that BRCA1 status may not be the only indicator for PARPi sensitivity in breast cancer. This evidence concerns the gene BRCA1 and breast cancer.