However, BCC of DMBA/TPA-treated Ptchf/f CD4Cre skin (for experimental set-up, see Figure 5A) exclusively occur at the IFE in HF-near regions (Figure 5B,C) and express K5 (Figure 5C) but never grow as tumors of the bulge or secondary hair germ like in Ptchf/f K5CreERT skin [13] (Appendix A, Figure A3). This evidence concerns the gene KRT5 and skin basal cell carcinoma.