Biomarkers in Clinical Research

Biomarkers for Clinical Research

• Biomarkers can be classified into two categories: endobiotic (normally present in the human body and needed for healthy bodily function, e.g., cholesterol) and xenobiotic (foreign to the human body, e.g., lead).
• Biomarkers can be used for diagnostic, prognostic, susceptibility, exposure, or outcome purposes.

Clinical Use of a Biomarker

• Biomarkers have a spectrum of use and specifications in clinical trials, including infectious and non-communicable diseases.
• Examples of biomarkers include circulating endothelial cells (CEC), circulating endothelial cell progenitors (CECP), and others.

Biomarkers in Cancer

• Biomarkers can be used in cancer research to identify surrogate endpoints.
• Surrogate endpoints are laboratory measures that substitute for clinically meaningful endpoints.
• Examples of surrogate endpoints include tumor size and histological cancer staging.

Characteristics of a Surrogate Endpoint

• A biomarker can be an indicator of a normal biological process, a pathogenic process, a pharmacologic response to a therapeutic intervention, or an interaction between a biological system and a health hazard.
• Biomarkers can reflect pathophysiological effects, concentration of agents, or biological effects.

Biomarkers and Measurement Error

• Measurement error occurs when there is a difference between the measured biomarker and the true exposure.
• True exposure refers to the underlying biological or external factor that the biomarker is meant to measure.

Sources of Error in Biomarkers

• Common sources of error in biomarkers include variability and/or error introduced during specimen collection, processing, and storage.

Biomarkers for Environmental and Occupational Research

• Environmental agents include contaminants of the general environment, agents used in the personal environment, and toxic agents in specific environments.
• Exposure to environmental agents can be unknown or un-sensed by individuals, making accurate documentation challenging.

Individual vs. Population Measurement of Present Exposures

• Population level measurement involves an ecological approach, making assumptions about individual behaviors that influence exposure.
• Individual measurement uses personal sensors and takes into account personal behavior, but may not be acceptable for prolonged periods of time.

Biomarkers in Daily Life

• Biomarkers are increasingly being used in people's daily lives.

Role of Dose and Route of Exposure

• The potential dose is the amount of a chemical ingested, inhaled, or applied to the skin.
• The applied dose is the amount absorbed or deposited in the body.
• The internal dose is the amount available for interaction with biologically significant molecular targets.
• The biologically effective dose is the amount that has interacted with a target site and alters a physiologic function.