PSME3 and neoplasm: Some other human breast cancer key genes were also analyzed in feline mammary carcinomas at the sequence level (e.g., the tumor suppressor and cell cycle regulatory genes p21 WAF1 and p27 Kip1 by Mayr et al. in 2000 [52] or the oncogene RAS, specifically N-, Ki-, and Ha-ras performed by Watzinger et al. [53]), but the search for any mutational signal in the latter referred genes failed.