The level of evidence required for informed decision making about genetic testing depends on the circumstances of testing. Evidence from a sample of high-risk families may be sufficient to provide useful information for testing decisions among people with similar family histories but is likely to be insufficient to make early recommendations for, or decisions about, testing in families with less dramatic histories or in the general population. Even among people with similar family histories, however, other contributing genes or different exposures could modify the effect of a gene mutation in different families. In evaluating evidence, the most important consideration is the relevance of the available data to the patient for whom a genetic assessment is being considered. In summaries addressing the cancer risk associated with genetic polymorphisms and mutations, the study populations used for each risk assessment will be noted, according to the following categories.
- Proxy for population-based. (The study population selected is assumed to be generally representative of the population from which it is drawn. For example, people participating in a community-based Tay-Sachs screening program, as a proxy for people of Jewish descent.)
- Public recruitment of volunteers (e.g., using a newspaper advertisement).
- Sequential case series.
- Convenience sample.
- An affected family or several families.