Three of 6 cases harbored the same K-ras codon 12 mutation as the PanINs in orthotopic pancreas, and a similar pattern of p53, cyclin D1, and p16 expression was observed between heterotopic and orthotopic pancreas in all 6 cases.
These data demonstrate that overexpression of p21(WAF1/CIP1) occurs early in the development of PanIN, before aberrations in p53, cyclin D1, and DPC4/Smad4 expression. p21(WAF1/CIP1) overexpression, independent of p53 and/or DPC4/Smad4 expression, may reflect increased Ras activity, either directly through activating K-ras mutations or as a consequence of HER-2/neu (ERBB2) overexpression, both of which are common in PC and in early events in the development of PanIN.