ERBB2 and breast cancer: Although ∆Np63/p40 has pro‐survival functions in mammary stem/progenitor cells 40 and in basal/HER2‐driven experimental breast cancers 15, 16, we found that a ΔNp63/p40+ cell population was not associated with poor patient survival in ER+ or HER2+ breast cancers, mirroring previous observations 18, 34.