The incidence of ER+/HER2+ cancers that contain a ΔNp63/p40+ tumour cell subpopulation is also uncertain, partly due to the presence of ΔNp63/p40 in normal myoepithelium, which is a common component of surgically removed human breast cancers 4, 25, 26. This evidence concerns the gene ESR1 and breast carcinoma.