LMP2 knockout mice exhibit a defect in proteasome function, and LMP2−/− female mice are shown to develop uterine leiomyosarcomas, with a disease prevalence of 36% by 12 months of age (Van Kaer et al. 1994; Hayashi and Faustman, 2002). This evidence concerns the gene PSMB9 and leiomyosarcoma.