There are several outcome metrics that have been validated as surrogate markers to predict mortality reduction by retrospective study of data from the randomized controlled trials involving film-screen mammography conducted several decades ago. These surrogate markers include tumor size, rate of node negativity, tumor stage, and rate of interval cancers. There already is ample evidence described in the ACR letter to insurers involving three of the four surrogate markers (all except for rate of interval cancers).
Since all of the surrogate markers are valid predictors of mortality reduction, it is not necessary to have evidence for the fourth marker when we already have sufficient evidence for three of the markers. Furthermore, the demonstration of technology-specific additional decrease in the rate of interval cancers has not been required to justify insurance coverage for either FFDM or any other breast imaging technology.