Serological markers of cancer and their applications in clinical trials.

Strategies for the prevention of cancer include those aimed at reducing the incidence of cancer (primary prevention) and cancer mortality through early detection of tumors (secondary prevention). The efficacy of prevention interventions is evaluated by clinical trials. The conduct of clinical trials is aided by the use of serological indicators of the carcinogenic process measured using plasma or red or white blood cells. The accessibility and acceptability of obtaining blood samples for the measurement of serological markers of carcinogenesis permit widespread applications in the conduct of clinical trials. Serological markers must be shown to be valid and reliable before their use. Serological markers identify a variety of stages in the process of carcinogenesis such as inherited or acquired susceptibility to cancer, environmental exposures to carcinogens, biological effects of exposures, and the presence of preinvasive or invasive cancer. Serological markers may be used in clinical trials to select high risk but disease-free individuals for participation in clinical trials based on susceptibility factors or carcinogenic exposures. Other uses of serological markers include monitoring adherence to interventions and establishing trial outcomes of intermediate cancer end points or incident invasive disease. Examples of these applications are discussed. Serological markers of carcinogenesis have widespread applications in clinical research and potentially for clinical practice. Currently, the only limitation to their widespread use is the availability of validated serological markers. Because of the ease and acceptability of their use, research into the development of serological markers should continue. Methods for quickly validating serological markers should be developed in order to aid the transition to clinical applications.