CDKN1B and prostate intraepithelial neoplasia: Thus, the incidence of PIN was similar in placebo- and 9cRA-treated p27+/+ and p27-/- mice, 13% in both placebo groups and 40% and 60% in treated animals, respectively (p < 0.5); even in 9cRA-treated mice a tendency for increase of PIN multiplicity was observed, rising from 0.7 ± 0.3 in placebo to 1.5 ± 1.1 (p < 0.1).