In the phase 2, PACE trial, the combination of #palbociclib plus fulvestrant did not improve significantly PFS compared with fulvestrant alone in patients with metastatic HR+/HER2- #breast_cancer who had progression on a prior CDK4/6 inhibitor.

In this trial that was presented at SABCS 2022 by Mayer et al, 220 patients with metastatic HR+/HER2- breast cancer were randomized in a 1:2:1 ratio to receive fulvestrant alone, fulvestrant plus palbociclib, or fulvestrant plus palbociclib and avelumab. Patients had to have disease progression on endocrine therapy and a CDK4/6 inhibitor in the metastatic setting. The primary endpoint was PFS of fulvestrant plus palbociclib vs fulvestrant alone.

After a median follow-up of 23 months, adding palbociclib didn’t improve PFS with the HR for PFS 1.11 (P = .62) with median PFS of 4.8 months with Fulvestrant alone versus 4.6 months in the combination arm. Regarding the response rates in patients with measurable disease, was 10.8% for fulvestrant alone versus 13.7% for fulvestrant plus palbociclib. Regarding overall survival (OS), there was no significant difference, with the median OS of 27.5 months versus 24.6 months, respectively.

Interestingly, the triplet arm adding avelumab showed promising results with median PFS of 8.1 months and median OS of 42.5 months.