Cell cycle regulators and their abnormalities in breast cancer

One of the main properties of cancer cells is their increased and deregulat ed proliferative activity. It is now well known that abnormalities in many positive and negative modulators of the cell cycle are frequent in many can cer types, including breast carcinomas. Abnormalities such as defective fun ction of the retinoblastoma gene and cyclin-dependent kinase inhibitors (fo r example, p16, p21, and p27), as well as upregulation of cyclins, are ofte n seen in breast tumours. These abnormalities are sometimes coincidental, a nd newly described interplays between them suggest the existence of a compl ex regulatory web in the cell cycle.