Since OGF depresses DNA synthesis and subsequent cell/tissue growth in human pancreatic cancer cells in vitro and in xenografts transplanted into nude mice [3], and flow cytometry studies indicate that the Go/G1 of the cell cycle is altered [5], the question arises as to the mechanism of peptide action on the cell cycle in cancers that have a mutation/deletion of p16. This evidence concerns the gene PENK and cancer.