The p63 protein is a member of the p53 family, which also includes p73. The p63 gene encodes multiple isoforms: isoform containing a potent amino-terminal transactivation domain (Tap63 isoforms) and isoforms lacking that region (ΔNp63 isoforms). Although the Tap63 isoforms can transactivate p53 target genes, p63 is not considered as a tumor suppressor. The ΔNp63 isoforms act in a dominant-negative manner by competing for the p53 target genes and indirectly promote cell growth by counteracting the apoptosis and cell cycle arrest activation by Tap63 isoforms and p53.P63 may be seen in non-invasive epithelial tumors, whereas loss of p63 expression may be found in more invasive tumors suggesting that loss of p63 accelerates tumorigenesis and metastasis. The predominant localization of p63 protein is in basal cells of normal epithelia in ectocervix, esophagus, prostate, skin, tonsil, urothelium, and vagina and in basal cells in glandular structures of breast, bronchi and prostate. p63 protein is also expressed in myoepithelial cells of the breast.