Therefore, the search for new markers, especially among cell cycle-regulatory molecules, is a high priority, both in terms of prognostication and for identification of novel targets. p21 regulates the outcome of the p53 response to DNA damage, as might occur after administration of a chemotherapeutic agent, and we have shown that attenuation of p21 using an antisense oligodeoxynucleotide (ODN) inhibits cell proliferation in vitro and decreases growth of Met-1 mammary carcinomas in mice.