Evidence Assessment for PDQ® Cancer Information for Health Professionals

The guiding principle of the editorial process for the PDQ health professional cancer information summaries is that evidence, linked to an evaluation of the quality of the evidence, takes precedence over a consensus of current practice. To develop and maintain the PDQ cancer information summaries, NCI uses an ongoing, systematic method for assessing the published literature related to the use of cancer-related interventions. To aid in these evaluations, formal criteria are used to classify, or rank, the strength of the evidence from published research studies.

NCI seeks out the strongest published evidence available.

• Reports of randomized controlled clinical trials and meta-analyses of randomized controlled clinical trials are used whenever possible.
• Other study designs, such as non-randomized trials, cohort studies, and case series, will be considered for rare cancers and in cases where randomized controlled trials are not available, or instances where the literature on a topic is sparse.
• Case reports are rarely considered.

In some cases, the description of the results in the PDQ cancer information summary is accompanied by cautionary statements about the limited strength and potential biases of the reported evidence.

Listed below are links to detailed descriptions of the criteria used to evaluate published studies for each type of literature:

• Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®)
• Levels of Evidence for Supportive and Palliative Care Studies (PDQ®)
• Levels of Evidence for Cancer Genetics Studies (PDQ®)
• Levels of Evidence for Human Studies of Integrative, Alternative, and Complementary Therapies (PDQ®)
• Levels of Evidence for Cancer Screening and Prevention Studies (PDQ®)