Interestingly, 9cRA did not significantly affect cell proliferation in non-PIN cells, which have low proliferative activity, but significantly reduced proliferating cells in PIN of both p27+/- and p27-/- mice, indicating that 9cRA may have the potential to suppress preferentially pre-malignant stages of prostate carcinogenesis in men independent of the levels of p27Kip1 expression. The gene discussed is CDKN1B; the disease is prostate intraepithelial neoplasia.