To determine the effect of Men1 inactivation on prostate cancer development in mice, we followed a cohort of 47 male mutant mice (Men1+/-) and 23 wild-type (Men1+/+) age-matched littermate mice from 18 to 26 months of age, based on a previous study that showed no prostate cancer in younger mice [6]. The gene discussed is MEN1; the disease is Familial prostate cancer.