Abstract
This perspective on Kim et al. (beginning on p. 148 in this issue of the journal) examines the value of the Ki-67 proliferation index as a surrogate end point in early-phase clinical lung cancer prevention trials. The clinical trial of Kim et al. shows an effect of the cyclooxygenase-2-selective inhibitor celecoxib at a high dose on Ki-67 expression in the normal bronchial epithelia of current and former smokers. The critical issue of how these data can be used to further drug development is discussed.