Apoptosis in human non-melanoma skin cancer

Cancer development is a complex, multistage process. Apoptosis has been found to modulate the stages of initiation, promotion, and progression in the stepwise formation of skin cancer. Apoptosis-regulatory proteins include those that block apoptosis, such as bcl-2 and bcl-x and the recently described apoptosis inhibitor survivin, whilst a related protein, bax, promotes apoptosis. Cell cycle regulatory proteins include those associated with growth arrest; i. e., p21 wafl, p53, and those associated with proliferation, i. e., Ki-67. If the tumour cells constitute the target for genetic changes triggered by environmental physical or chemical mutagenic agents, such as UV rays, the apoptotic rate is much higher (mean value: 40 %). These changes can be the result of newly selected mutated neoplastic cell clones which have more aggressive biological behaviour. Irradiation and many drugs used to treat cancers are primarily genotoxic, either directly or by disrupting DNA metabolism, and at therapeutic doses they trigger apoptosis in the target cells. It is of a great importance to explore the process of apoptosis to work out more effective methods of cancer prevention and therapy.