Prostate adenocarcinoma, defined as penetration of malignant prostate epithelial cells through the basement membrane of the prostate gland into the surrounding stroma, was often observed in APT121;Mdm2+/+ mice, while the majority of the APT121;Mdm2C305F/C305F mice only developed mPIN (mouse prostatic intraepithelial neoplasia), with few examples of well-differentiated adenocarcinoma (Figure 1C ). The gene discussed is MDM2; the disease is prostate intraepithelial neoplasia.