This prospect raises many questions. How does the research community ensure that appropriate cohorts and sample repositories are available once the technologies have matured to the point of routine application? What are the limitations of using existing cohorts for toxicogenomic studies? Given the limitations of existing cohorts with respect to the informed consent, sample collection, and data formats, how should future population-based studies be designed? What is the ideal structure of a consortium that would assemble such a cohort, collect the necessary samples and data, and maintain repositories? Consideration of these questions begins with an examination of the current state of affairs.

Current Practices and Studies

Central to all population-based studies are identifying suitable cohorts, recruiting participants, obtaining informed consent, and collecting the appropriate biologic samples and associated clinical and epidemiologic data. Collecting, curating, annotating, processing, and storing biologic samples (for example, blood, DNA, urine, buccal swabs, histologic sections) and epidemiologic data for large population-based studies is a labor-intensive, expensive undertaking that requires a significant investment in future research by the initial study investigators. As a result, study investigators have reasonable concerns about making biologic samples available for general use by others in the scientific community. With the notable exception of immortalized lymphocyte cell lines that provide an inexhaustible resource from the blood of study participants, biologic specimens represent a limited resource and researchers often jealously guard unused samples for future use once the “ideal” assays become available. It is not unusual for institutions with sizeable epidemiology programs to have hundreds of thousands of blood, serum, lymphocyte, and tumor samples in storage that are connected to clinical data as well as information on demographics, lifestyle, diet, behavior, and occupational and environmental exposures.

In addition to cohorts and samples collected as part of investigator-initiated studies and programs, sample repositories have also been accrued by large consortia and cooperative groups sponsored by the public and private sectors. An example of publicly sponsored initiatives in the area of cancer research and national and international sample and data repositories is the National Cancer Institute (NCI)-sponsored Southwest Oncology Group (SWOG), one of the largest adult cancer clinical trial organizations in the world. The SWOG membership and network consists of almost 4,000 physicians at 283 institutions throughout the United States and Canada. Since its inception in 1956, SWOG has enrolled and collected samples from more than 150,000 patients in clinical trials.

Examples in the area of cancer prevention are the NCI-sponsored intervention trials such as the CARET (beta-Carotene and Retinoic Acid) study for prevention of lung cancer, and the Shanghai Breast Self Exam study conducted in factory workers in China. CARET was initiated in 1983 to test the hypothesis



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