Llombart-Cussac A, Pérez-García JM, Bellet M, et al. - Patients with endocrine-sensitive, hormone receptor–positive, ERBB2-negative advanced breast cancer experienced no improvement in progression-free survival with fulvestrant-palbociclib treatment vs letrozole-palbociclib, though fulvestrant-palbociclib showed significant antitumor activity. This corroborates letrozole as the preferred palbociclib partner in such cases.

• This is an international, randomized, open-label, phase 2 clinical study with 486 patients with endocrine-sensitive, hormone receptor–positive, ERBB2-negative advanced breast cancer.

• Patients were randomized (1:1 ratio) to receive palbociclib with either fulvestrant or letrozole.

• Fulvestrant-palbociclib conferred a median investigator-assessed progression-free survival of 27.9 months, in comparison which was 32.8 months for letrozole-palbociclib (hazard ratio, 1.13), a difference that was not statistically significant.

• Objective response rate (46.5% vs 50.2%) and 3-year overall survival rate (79.4% vs 77.1%) did not differ significantly between fulvestrant-palbociclib vs letrozole-palbociclib, respectively.

• Comparable grade 3-4 adverse events were evident among treatment groups, with no new safety signals and no treatment-related deaths reported.