p63 is a tumor suppressor protein that is very similar to p53 in structure and function, while being homologous to p73. p63 is important in development and differentiation, and has been identified as a useful marker for distinguishing between lung squamous cell carcinomas and adenocarcinomas. 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.