p63, a homolog of the tumor suppressor p53, has been identified in basal cells in the epithelial layers of a variety of tissues, including epidermis, cervix, urothelium, breast and prostate (1). p63 was detected in nuclei of the basal epithelium in normal prostate glands; however, it was not expressed in malignant tumors of the prostate (2). 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) (3-4). p63 has also been shown to be a sensitive marker for lung squamous cell carcinomas (SqCC), with reported sensitivities of 80-100% (5-8). Specificity for lung SqCC, vs. lung adenocarcinoma (LADC), has been reported to be approximately 70-90%, as positive staining with p63 has been typically observed in 10-30% of LADC cases (5-8). In breast tissue, p63 has been identified in myoepithelial cells of normal ducts (9). Reports have described the utility of p63 in a panel of IHC markers for the assessment of breast lesions, due to the differential expression of the luminal vs. basal and myoepithelial markers (9-11).