SHH and cancer: Whereas conditional expression of oncogenic SmoM2 in the mouse prostate epithelium does not lead to mouse prostatic intraepithelial neoplasia (mPIN) or cancer (Mao et al., 2006), xenograft experiments using PCa cell lines have indicated a pro-tumor effect of HH signaling (Fan et al., 2004; Karhadkar et al., 2004), and one study using retroviral expression of SHH in the prostate reported cancer formation (Chen et al., 2006).