p63 is a tumor suppressor protein that is very similar to p53 in structure and function, while being homologous to p73. P63 is identified in basal cells in the epithelial layers of a variety of tissues, including epidermis, cervix, urothelium, breast and prostate. p63 is important in development and differentiation, and has been identified as a useful marker for distinguishing between lung squamous cell carcinomas and adenocarcinomas. p63 has been shown to be a promising complementary basal cell specific marker to High Molecular Weight-Cytokeratin (HMW-CK), for the differential diagnosis of benign prostatic lesions and prostatic carcinoma. Anti-p63 is also used to differentiate between benign and malignant prostate and breast lesions, due to its labeling of the nuclei of myoepithelial cells in both tissue types.