TP63 and cancer: To investigate whether any receptor‐positive breast cancer cell lines contain a similar population of ∆Np63/p40+ cells, we initially studied publicly available RNA‐Seq data of human cancer cell lines (https://www.ebi.ac.uk/arrayexpress E‐MTAB‐2706), containing data for 68 human breast cancer cell lines (see supplementary material, Figure S1).