MKI67 and prostate intraepithelial neoplasia: Levels of proliferation were 9 fold higher in Brca2F/F;Trp53F/+;PBCre4 PIN lesions (3.5% Ki-67 positive cells vs 0.4% in control), and dramatically increased by 30 fold in Brca2F/F;Trp53F/F;PBCre4 HG PIN lesions (12% Ki-67 positive cells vs 0.4% in control) (Figure 4A).