- K Harada: Oral Diseases Group, Unit of Oral Surgery and Medicine, Dundee Dental Hospital and School, Park Place, DD1 4HN, UK. kharada@bad.dundee.ac.uk
p21, also known as WAF1, Cip1, Sdi1, Mda 6 and Cap20 is a cell cycle protein that regulates and can arrest the cell cycle in G1 or S phase (either dependent or independent of p53). Its role may be pivotal in many cell processes including differentiation and apoptosis. This brief overview provides a summary of its presently known functions and indicates areas for further research, particularly in relation to oral malignant disease. Greater understanding of its role may lead to therapeutic advances in the management of malignant disease.