Sara Marín-Liébana

PURPOSE: Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors plus endocrine therapy (ET) represents the standard first-line treatment for patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HER2-negative) advanced breast cancer (ABC). However, there is no definitive consensus on the preferred second-line treatment option. The PALMIRA trial investigated whether palbociclib rechallenge with an alternative ET would improve the antitumor activity in patients progressing after a first-line palbociclib-containing regimen. METHODS: This international, randomized, open-label, phase II study enrolled 198 patients with hormone receptor–positive/HER2-negative ABC with disease progression after first-line palbociclib plus ET (aromatase inhibitor or fulvestrant). Patients were eligible if they showed clinical benefit to the previous regimen (response or stable disease ≥24 weeks) or had progressed on a palbociclib-based therapy in the adjuvant setting. Patients were randomly assigned (2:1 ratio) to either palbociclib rechallenge plus second-line ET (fulvestrant or letrozole) or second-line ET alone. Stratification factors were previous ET and visceral involvement. The primary end point was investigator-assessed progression-free survival (PFS). RESULTS: Between April 2019 and October 2022, 136 and 62 patients were randomly assigned to palbociclib plus ET or ET alone, respectively. Median investigator-assessed PFS was 4.9 months (95% CI, 3.6 to 6.1) with palbociclib plus ET versus 3.6 months (95% CI, 2.5 to 4.2) with ET alone (hazard ratio, 0.84 [95% CI, 0.66 to 1.07]; P = .149). Grade ≥3 treatment-emergent adverse events were higher with palbociclib plus ET (47.4% v 10.0%), without new safety signals. CONCLUSION: Palbociclib rechallenge plus an alternative ET did not significantly improve PFS compared with ET alone in patients with hormone receptor–positive/HER2-negative ABC progressing on a first-line palbociclib-based ET regimen.

In triple-negative (TNBC) and human epidermal growth factor receptor 2-positive (HER2+) breast cancer patients, neoadjuvant systemic therapy is the standard recommendation for tumors larger than 2 cm. Monitoring the response to primary systemic therapy allows for the assessment of treatment effects, the need for breast-conserving surgery (BCS), and the achievement of pathological complete responses (pCRs). In estrogen receptor-positive/HER2-negative (ER+/HER2-) breast cancer, the benefit of neoadjuvant strategies is controversial, as they have shown lower tumor downstaging and pCR rates compared to other breast cancers. In recent decades, several gene expression assays have been developed to tailor adjuvant treatments in ER+/HER2- early breast cancer (EBC) to identify the patients that will benefit the most from adjuvant chemotherapy (CT) and those at low risk who could be spared from undergoing CT. It is still a challenge to identify patients who will benefit from neoadjuvant systemic treatment (CT or endocrine therapy (ET)). Here, we review the published data on the most common gene expression signatures (MammaPrint (MP), BluePrint (BP), Oncotype Dx, PAM50, the Breast Cancer Index (BCI), and EndoPredict (EP)) and their ability to predict the response to neoadjuvant treatment, as well as the possibility of using them on core needle biopsies. Additionally, we review the changes in the gene expression signatures after neoadjuvant treatment, and the ongoing clinical trials related to the utility of gene expression signatures in the neoadjuvant setting.