p63 is a homolog of the tumor suppressor p53. It is identified in basal cells in the epithelial layers of a variety of tissues, including epidermis, cervix, urothelium, breast and prostate. p63 was detected in nuclei of the basal epithelium in normal prostate glands; however, it was not expressed in malignant tumors of the prostate. As a result, p63 has been reported as a useful marker for differentiating benign from malignant lesions in the prostate, particularly when used in combination with markers of high molecular weight cytokeratins and the prostate-specific marker AMACR (P504S). p63 has also been shown to be a sensitive marker for lung squamous cell carcinomas (SqCC), with a sensitivity of ~90%. Specificity for lung SqCC, vs. lung adenocarcinoma (LADC), is approximately 80%. In breast tissue, p63 has been identified in myoepithelial cells of normal ducts.