In addition, the synthetic vulnerability of PTEN loss and pharmacologic Mcl-1 inhibition has been explored in the context of PTEN-deficient models of glioblastoma (54), but our study is the first to demonstrate that both PIK3CA mutations and PTEN loss in breast cancer cells can induce resistance to Bcl-xL inhibitor–mediated radiosensitivity. This evidence concerns the gene MCL1 and breast cancer.