Dalpiciclib or placebo plus fulvestrant in hormone receptor-positive and HER2-negative advanced breast cancer: a randomized, phase 3 trial.

Blockade of the cyclin-dependent kinase 4 and 6 pathway has been shown to be effective in the treatment of hormone receptor-positive advanced breast cancer (ABC). We report the interim results of DAWNA-1 ( NCT03927456 ), a double-blind, randomized, phase 3 trial of dalpiciclib (a new cyclin-dependent kinase 4 and 6 inhibitor) plus fulvestrant in hormone receptor-positive, HER2-negative ABC with disease progression after endocrine therapy. A total of 361 patients were randomized 2:1 to receive dalpiciclib plus fulvestrant or placebo plus fulvestrant. The study met the primary end point, showing significantly prolonged investigator-assessed progression-free survival with dalpiciclib plus fulvestrant versus placebo plus fulvestrant (median = 15.7, 95% confidence interval (CI) = 11.1-not reached versus 7.2, 95% CI = 5.6-9.2 months; hazard ratio = 0.42, 95% CI = 0.31-0.58; one-sided P < 0.0001 (boundary was P ≤ 0.008)). The most common grade 3 or 4 adverse events with dalpiciclib plus fulvestrant were neutropenia (84.2%) and leukopenia (62.1%). The incidence of serious adverse events was 5.8% with dalpiciclib plus fulvestrant versus 6.7% with placebo plus fulvestrant. Our findings support dalpiciclib plus fulvestrant as a new treatment option for pretreated hormone receptor-positive, HER2-negative ABC.