As disease-modifying therapies near realization, there are concerns about the criteria by which these therapies will be judged. It is not yet clear what kind of evidence (clinical, biomarker, or otherwise) will be required to support a disease-modifying claim. When such a drug is approved, regulators must be certain that the claims in the label are factual and unambiguous, yet a definition for “disease modification” remains to be established. One strong potential definition is: “a therapy that affects the underlying pathology and structure of the disease”. However, this is only one possibility, and a consensus definition must be codified before criteria to evaluate it can be determined.

There is room for informed speculation, however. Criteria to evaluate disease-modifying effects have been proposed, and typically involve one of two approaches (neither of which has yet been endorsed by regulators). The first is a clinical approach, in which clinical designs are employed that would ideally force a conclusion that a drug has a disease-modifying effect. In one proposed design, patients would be randomized to drug or placebo for an appropriate duration. At the end of that period, and if a difference in outcome between drug and placebo on an appropriate clinical measure or measures has been achieved, patients originally randomized to drug would then be treated with placebo, while patients originally treated with placebo would remain on placebo.