PTCH1 and skin basal cell carcinoma: Consistently, mice with Ptch1 mutation are susceptible to develop MB, especially in those with additional depletion in p53 allele or in homozygous ND2:SmoA1 (Smo activation mutation) transgenic mice, and develop UV-induced BCC (59–62), suggesting that Hh signaling pathway is a major driver in the development of these tumors.