ERBB2 and breast cancer: In order to explore a possible role of ΔNp63 as an effector of TGFβ signaling in the regulation of stemness, we analyzed the sphere forming capacity of HCC1954 HER2+ breast cancer cells, which express only the ΔNp63α isoform, and virtually no TAp63 (EV, data not shown and [31, 32]), before and after ΔNp63 depletion, using siRNA against all p63 isoforms or ΔNp63 specific siRNA, and subsequent stimulation by TGFβ.