Level of scientific evidence underlying recommendations arising from the National Comprehensive Cancer Network clinical practice guidelines.

PURPOSE: The level of scientific evidence on which the National Comprehensive Cancer Network (NCCN) guidelines are based has not been systematically investigated. We describe the distribution of categories of evidence and consensus (EC) among the 10 most common cancers with regard to recommendations for staging, initial and salvage therapy, and surveillance.
METHODS: NCCN uses a system of guideline development distinct from other major professional organizations. The NCCN definitions for EC are as follows: category I, high level of evidence with uniform consensus; category IIA, lower level of evidence with uniform consensus; category IIB, lower level of evidence without a uniform consensus but with no major disagreement; and category III, any level of evidence but with major disagreement.
RESULTS: Of the 1,023 recommendations found in the 10 guidelines, the proportions of category I, IIA, IIB, and III EC were 6%, 83%, 10%, and 1%, respectively. Recommendations with category I EC were found in kidney (20%), breast (19%), lung (6%), pancreatic (6%), non-Hodgkin's lymphoma (6%), melanoma (6%), prostate (4%), and colorectal (1%) guidelines. Urinary bladder and uterine guidelines did not have any category I recommendations. Eight percent of all therapeutic recommendations were category I. Guidelines with the highest proportions of category I therapeutic recommendations were for breast (30%) and kidney (28%) cancers. No category I recommendations were found on screening or surveillance.
CONCLUSION: Recommendations issued in the NCCN guidelines are largely developed from lower levels of evidence but with uniform expert opinion. This underscores the urgent need and available opportunities to expand evidence base in oncology.