The molecular biology of retinoblastoma.

Retinoblastoma, a rare pediatric eye tumor, has served as an important model for the heritable predisposition to cancer. The retinoblastoma protein, Rb, functions as a tumor suppressor by controlling progression through the cell cycle. Rb function is regulated primarily by its phosphorylation state, which is determined by the complex interaction of multiple kinases and their inhibitors that together form the 'Rb pathway'. This pathway has been found to be functionally inactivated in almost all types of cancer. Despite recent advances in our understanding of Rb function, the precise role of Rb loss in the development of retinoblastoma remains unclear. Recent work in genetically altered mice has suggested that an additional mutation in another gene is required for retinal tumor formation. An alternative model presented here is based on the noncell-autonomous functions of Rb contributing to tumorigenesis.