As MASTL inhibition reduces cell viability in various cancer cells [13–15] and targeting mitotic kinases such as PLK1 preferentially induces apoptosis in cancer cells compared to in non-transformed normal cells [3, 4], we expected that the inhibition of MASTL would induce cell death selectively in breast cancer cells and not in non-transformed normal cells. The gene discussed is MASTL; the disease is breast cancer.