Multicenter phase 3 trial of bireociclib plus fulvestrant in advanced breast cancer after endocrine progression: final analysis of BRIGHT-2

The phase 3 BRIGHT-2 trial, at 64 centers in China, randomized patients with HR-positive, HER2-negative advanced breast cancer (aBC) after progression on endocrine therapy 2:1 to bireociclib plus fulvestrant (n=204) or placebo plus fulvestrant(n=101). Interim analysis demonstrated the efficacy of bireociclib plus fulvestrant. Final analysis of the trial, with an additional 11-month follow-up, has now been published. After a median follow-up of 19 months (IQR 18.5-19.6) the median progression-free survival (PFS) was 14.7 months with bireociclib plus fulvestrant compared with 7.3 months with placebo plus fulvestrant (HR 0.54; p<0.001), with objective response rate 45.6% versus 14.9%, respectively, and median duration or response not reached versus 13.1 months, respectively. Safety was consistent with profiles of known CDK4/6 inhibitors. Subgroup analyses across multiple patients characteristics showed consistent PFS improvements with bireociclib versus placebo. The authors conclude that the final analysis of BRIGHT-2 confirmed improved PFS with the addition of bireociclib to fulvestrant, with manageable safety, among patients with HR+/HER2- aBC with progression after endocrine therapy.