Cancer and the dynamics of neurodegenerative processes.

The term neurodegenerative denotes a process rather than a state. In contrast, most research on such disorders, whether clinical or experimental, represents only a slice of time. Their progressive nature is mostly confined to speculation instead of being codified in research protocols. Research on cancer, also a degenerative disease, is much more often framed in terms of process. Part of the difference is accounted for by the impact of quantitative modeling, which enjoys a long history in both basic and clinical cancer research and which originated in attempts to describe and understand tumor development. Analogous questions are posed by neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Among the issues that modeling could help to clarify are the properties and sources of the age-specific incidence rate, which resembles that for cancer, and the pharmacokinetics governing the toxic products of neurotransmitter metabolism. Neurodegenerative disorders maintain a research advantage because functional measures, mostly inaccessible to cancer investigators, serve as the ultimate index of progression. Their exploitation, however, in longitudinal studies remains inadequate.