Contrarily to BCC in Ptchf/f CD4Cre skin, and similar to BCC from Ptchf/f K5CreERT, BCC from DMBA/TPA-treated Ptch+/− mice arise from HF and IFE (Figure 5D,E; for a comparison of BCC/mm skin in DMBA/TPA-treated Ptchf/f CD4Cre and Ptch+/− mice, see Appendix A, Figure A4) and stain positive for K5 (Figure 5E). Here, KRT5 is linked to skin basal cell carcinoma.