Our attempts to suppress the intracellular CSK actions by dominant-negative CSK as reported by Rengifo-Cam et al. were unsuccessful due to nonspecific induction of apoptosis of MCF-7 cells, which express wild type p53 tumor suppressor protein as the majority of human ER+/PR+/HER2- breast cancers [56], [83]. This evidence concerns the gene ESR1 and breast cancer.