To assist readers in evaluating the results of human/clinical studies of complementary and alternative medicine (CAM) treatments for cancer, a scoring system has been devised that allows studies of individual treatments to be ranked according to the strength of their evidence (i.e., their level of evidence). Not all studies, however, are given a level of evidence score. To be eligible, a study must:

• Evaluate a therapeutic outcome or outcomes, such as tumor response, improvement in survival, or carefully measured improvement in quality of life.
• Be reported in a peer-reviewed scientific journal.
• Have its clinical findings published in sufficient detail that a meaningful evaluation can be made.

Evidence from studies that do not meet these requirements is considered extremely weak. In addition to scoring individual studies, an overall level of evidence assessment is usually made.

Because no study of the use of Essiac or Flor•Essence in humans has been reported in a peer-reviewed scientific journal, no level of evidence analysis is possible for these mixtures. The data that are available, however, do not support claims that Essiac and Flor•Essence can detoxify the body, strengthen the immune system, or fight cancer. At this time, evidence does not support the use of either Essiac or Flor•Essence in the treatment of cancer patients outside the context of well-designed clinical trials.

Separate levels of evidence scores are assigned to qualifying human studies on the basis of statistical strength of the study design and scientific strength of the treatment outcomes (i.e., endpoints) measured. The resulting two scores are then combined to produce an overall score. For additional information about levels of evidence analysis, refer to Levels of Evidence for Human Studies of Cancer Complementary and Alternative Medicine.

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