CDKN2A and cervical squamous intraepithelial neoplasia: Given that WT MEFs usually immortalize after induction of CIN (tetraploidy) (Atsumi et al., 2011; Ichijima et al., 2010) and subsequent mutations in the ARF/p53 pathway (Matheu et al., 2007; Osawa et al., 2013), these results imply that irradiation facilitated induction of CIN.