Patient-reported outcomes in the SERENA-6 trial of camizestrant plus CDK4/6 inhibitor in patients with advanced breast cancer and emergent ESR1 mutations during first-line endocrine-based therapy

Background: In SERENA-6, switching from aromatase inhibitor (AI) to camizestrant with continuation of CDK4/6 inhibitor (CDK4/6i) guided by emergence of ESR1 mutations (ESR1-mut) during first-line AI-CDK4/6i in patients with hormone receptor (HR)-positive advanced breast cancer (ABC) resulted in statistically significant and clinically meaningful improvement in progression-free survival compared with AI-CDK4/6i and reduction in the risk of deterioration in global health status (GHS)/quality of life (QoL) (hazard ratio 0.54). Here we report additional data from patient-reported outcomes (PROs). Patients and methods: Patients completed PRO questionnaires at pre-specified timepoints, including the European Organisation for Research and Treatment of Cancer (EORTC) oncology-specific EORTC Quality of Life Questionnaire Core 30 (QLQ-C30) and breast cancer-specific (QLQ-BR23) and Patient Global Impression of Treatment Tolerability (PGI-TT). All PRO endpoints and analyses were pre-defined, including secondary endpoints of time to deterioration (TTD) in pain, physical functioning, breast symptoms and arm symptoms. Results: EORTC QLQ-C30 and EORTC QLQ-BR23 baseline scores were similar between treatment arms. Switching to camizestrant-CDK4/6i delayed TTD and reduced the risk of deterioration in patient-reported cancer symptoms [pain (hazard ratio 0.57, 95% confidence interval 0.37-0.86), fatigue (0.75, 0.46-1.24), shortness of breath/dyspnoea (0.52, 0.28-0.93), breast symptoms (0.59, 0.28-1.24) and arm symptoms (0.69, 0.34-1.39)] and functioning [physical (0.74, 0.44-1.24), role (0.73, 0.48-1.10) and emotional (0.51, 0.29-0.87)] compared with AI-CDK4/6i. Most patients reported they were ‘not at all’ or ‘a little bit’ bothered by the side effects of cancer therapy across timepoints (e.g. week 2: 86% camizestrant-CDK4/6i versus 82% AI-CDK4/6i). Conclusions: Together with the clinical efficacy and manageable safety profile of camizestrant-CDK4/6i, and reduced risk of GHS/QoL deterioration, the PROs from the SERENA-6 trial support switching to this combination as a potential new treatment strategy to optimise and improve outcomes in patients with HR-positive/HER2-negative ABC and ESR1-mut emergence, ahead of disease progression, during first-line AI-CDK4/6i.