As used in clinical trials, it has been defined as a laboratory measurement or a physical sign used as a substitute for a clinically meaningful endpoint that measures directly how a patient feels, functions or survives. Changes resulting from a therapy on a surrogate endpoint are expected to reflect those obtained in a clinically meaningful or desired endpoint. Examples of surrogate endpoints include LDL cholesterol levels for myocardial infarction, blood pressure for the outcome of a stroke, and brain imaging of volumes of relevant structures in which shrinkage may be a sensitive surrogate marker to track progressive neurodegenerative diseases such as Alzheimer’s and Tay-Sachs, and certain childhood disorders that are often rare (e.g., Heller’s disease, a form of autism). One potential benefit of surrogate markers rather than clinical endpoints is that they may reduce the size, duration and costs of clinical trials. A reliance on surrogate markers may, however, lead to an excess of morbidity and mortality.
See Alzheimer’s disease, Autism, Causal pathway, Tay-Sachs disease