Palbociclib and Fulvestrant in Breast Cancer

To the Editor: The results of the survival analysis in the phase 3 (Palbociclib: Ongoing Trials in the Management of Breast Cancer [PALOMA]) PALOMA-3 trial reported by Turner et al. (Nov. 15 issue) 1 are of great interest. Although the trial prohibited crossover to palbociclib, 16% of the patients in the placebo–fulvestrant group received palbociclib after disease progression. This leads to a few concerns. First, because of the proven efficacy of cyclin-dependent kinases 4 and 6 (CDK4/6) antagonists in hormone-positive breast cancer, the observed survival benefit might have been obviated if crossover was actually permitted. Second, progression-free survival from the start . . .