Interestingly, proportions of pRb-positive cells and Ki-67–positive cells were significantly higher in PanINs developed in KCR mice compared with those in control KC mice (Supplemental Figure 2C), raising the possibility that RECK deletion results in increased proliferative potential of PanIN cells through E2F activation, thereby increasing the probability of tumor progression. Here, RB1 is linked to keratoconus.