PTCH1 and nevoid basal cell carcinoma syndrome: 107), rhabdomyosarcoma (Ref. 108) and developmental aberrations. Notably, full-blown BCCs are rarely seen in Ptch1+/− mice maintained in normal conditions, but lesions resembling BCCs develop when mice are exposed to ultraviolet (UV) or ionising radiations (Ref. 109). This observation is in agreement with the clinical course of BCC in BCNS patients, where BCCs occur preferentially on sun-exposed areas of the body (Ref. 110).