TP53 and cancer: Our data of qRTPCR demonstrated that exposure to Ca(OH)2NPs for 48 h trigger apoptosis of HepG2 cells through the concurrent marked upregulation of the apoptotic (p53 and Bax) genes’ expression level and a significant decrease in the anti-apoptotic Bcl2 gene expression level noticed after treatment of HepG2 cancer cells with Ca(OH)2NPs.