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Levels of Evidence for Cancer Genetics Studies (PDQ®): Genetics - Health Professional Information [NCI] - Use of Levels of Evidence

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Evidence Related to Cancer Prevention

Prevention is defined as a reduction in the incidence (or the rate) of new cancer, with the goal of reducing cancer-related morbidity and mortality. Examples of prevention strategies include smoking cessation, avoidance of excessive exposure to sunlight (ultraviolet) or ionizing radiation, surgical removal of an at-risk target organ before cancer develops, and use of medications (e.g., tamoxifen for breast cancer risk reduction).

For each prevention-related summary of evidence statement, the associated levels of evidence are listed. In descending order of strength of evidence, the five levels are as follows:

  1. Evidence obtained from at least one well-designed and well-conducted randomized controlled trial that has:
    1. A cancer endpoint.
      1. Mortality.
      2. Incidence.
    2. A generally accepted intermediate endpoint (e.g., large adenomatous polyps for studies of colorectal cancer prevention).
  2. Evidence obtained from well-designed and well-conducted nonrandomized controlled trials that have:
    1. A cancer endpoint.
      1. Mortality.
      2. Incidence.
    2. A generally accepted intermediate endpoint (e.g., large adenomatous polyps for studies of colorectal cancer prevention).
  3. Evidence obtained from well-designed and well-conducted cohort or case-control studies, preferably from more than one center or research group, that have:
    1. A cancer endpoint.
      1. Mortality.
      2. Incidence.
    2. A generally accepted intermediate endpoint (e.g., large adenomatous polyps for studies of colorectal cancer prevention).
  4. Ecologic (descriptive) studies (e.g., international patterns studies and migration studies) that have:
    1. A cancer endpoint.
      1. Mortality.
      2. Incidence.
    2. A generally accepted intermediate endpoint (e.g., large adenomatous polyps for studies of colorectal cancer prevention).
  5. Opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees (e.g., any of the above study designs using invalidated surrogate endpoints).

In assessing a genetic test (or other method of genetic assessment, including family history), the analytic validity, clinical validity, and clinical utility of the test need to be considered.[3]

Evidence Related to Treatment

For each treatment-related summary of evidence statement, the associated levels of evidence are listed. In descending order of strength of evidence, the five levels are as follows:

  1. Evidence obtained from randomized controlled trials.
  2. Evidence obtained from nonrandomized controlled trials.
  3. Evidence obtained from cohort or case-control studies.
    1. Total mortality (or overall survival from a defined time).
    2. Cause-specific mortality (or cause-specific mortality from a defined time).
    3. Carefully assessed quality of life.
    4. Indirect surrogates.
      1. Disease-free survival.
      2. Progression-free survival.
      3. Tumor response rate.
  4. Evidence from ecological, natural history, or descriptive studies.
  5. Opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees.

References:

  1. Woolf SH: Screening for prostate cancer with prostate-specific antigen. An examination of the evidence. N Engl J Med 333 (21): 1401-5, 1995.
  2. Winawer S, Fletcher R, Rex D, et al.: Colorectal cancer screening and surveillance: clinical guidelines and rationale-Update based on new evidence. Gastroenterology 124 (2): 544-60, 2003.
  3. Holtzman NA, Watson MS, eds.: Promoting Safe and Effective Genetic Testing in the United States: Final Report of the Task Force on Genetic Testing. Baltimore, Md: Johns Hopkins Press, 1998. Also available online. Last accessed February 04, 2013.
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WebMD Public Information from the National Cancer Institute

Last Updated: February 25, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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