Furthermore, in human and murine normal keratinocytes and non-melanoma skin tumors (e.g., papilloma, basal cell carcinoma, squamous cell carcinoma) CB1 and CB2 receptors were expressed and were required for the development of NMSC in vivo (Casanova et al., 2003; Zheng et al., 2008). Here, CNR1 is linked to papilloma.