Understanding the link between cancer and neurodegeneration

There is growing evidence that cancer shares a number of biological pathways with common neurodegenerative diseases of aging. In epidemiologic studies, Parkinson's and Alzheimer's disease seem to be associated with a decreased cancer risk. Genes associated with neurodegeneration have important functions in protein folding and processing, but often play a role in the cell cycle. Activation and deregulation of the cell cycle is a core feature of both diseases; in the neuron, the end result is apoptosis, while in the malignant cell, it is uncontrolled proliferation. Successful aging requires a careful balance between the forces that promote tissue renewal and those that suppress the cell cycle. Proteins such as p53 and Pin1 might explain why some individuals are relatively protected from cancer but at increased risk of neurodegeneration. This article reviews the available epidemiologic evidence linking neurodegenerative disease and cancer, discusses the cellular pathways and genes which might account for this unexpected relationship, and explores the potential therapeutic implications of this area of research.