Phase 2 trial of palbociclib, trastuzumab, and endocrine therapy for pretreated HER2-positive and PAM50 luminal advanced breast cancer

The Spanish multicenter phase 2 SOLTI-PATRICIA trial cohort C randomized 73 pretreated patients with HER2-positive, hormone receptor-positive, and PAM50 luminal A/B advanced breast cancer 1:1 to the triplet regimen of palbociclib, trastuzumab, and endocrine therapy (ET) or trastuzumab-based treatment of physician’s choice (TPC). In the TPC arm, 48.5% were treated with trastuzumab plus chemotherapy, 39.4% with trastuzumab emtansine, and 12.1% with trastuzumab plus ET. The primary endpoint was investigator-assessed progression-free survival. The triplet regimen was associated with a significantly better PFS compared with TPC (stratified HR 0.52; p=0.03). PFS rates after 24 months were 24.0% with the triplet regimen and 4.3% with TPC. The overall response rate was 18.9% and 7.1%, respectively. In the triplet group, grade ≥ 3 adverse events occurred in 61.5% of patients. No permanent discontinuation due to toxicity were reported. The authors conclude that the triplet combination was safe and significantly improved PFS compared with TPC in previously treated patients with HER2-positive, PAM50 luminal A/B advanced breast cancer.