NPM1 and breast cancer: By exploiting the interacting domain of the basic region (BR) of HEXIM1, which mediates the binding with NPM1 that is responsible for ubiquitination by the human double minute 2 protein to promote degradation, an innovative cytotoxic peptide fused with a cell-penetrating or breast cancer-specific peptide—the HEXIM1 BR peptide—was developed and found to trigger rapid specific cytotoxic killing of breast cancer cells [31].