Health-related quality of life with first- vs tweedelijns CDK4/6 inhibitor use in gevorderd breast cancer: results fr...

BACKGROUND: The SONIA trial demonstrated that addition of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) to first-line endocrine therapy (aromatase-inhibitor) was not superior in terms of progression-free survival after 2 treatment lines compared with addition to second-line (fulvestrant), while first-line use increased toxicity (74% more grade ≥3 adverse events) and costs. Understanding the impact of both treatment strategies on health-related quality of life (HRQOL) is critical to inform patient-centered treatment decisions. METHODS: HRQOL was assessed using the Functional Assessment of Cancer Therapy-Breast (FACT-B) and EuroQoL 5-dimensions 5-level questionnaires at up to 11 time points over the course of both treatment lines (follow-up) until SONIA treatment discontinuation. FACT-B total and subscale scores-including physical, social, emotional, functional well-being, and the breast cancer subscale-along with EuroQoL 5-dimensions 5-level scores were compared between treatment strategies using mixed linear regression models. Clinically meaningful differences were predefined as 7 points for the FACT-B total score and 2 points for subscales. RESULTS: Questionnaire completion rates for FACT-B were 88% at baseline and 75% during follow-up. No clinically or statistically significant differences in HRQOL were observed between treatment arms during follow-up. The estimated mean difference in FACT-B total score (CDK4/6i in second-line as reference) was -0.66 (95% confidence interval [CI] = -2.14 to 0.82; P = .39). Differences for subscales were similarly small. CONCLUSION: HRQOL was comparable between patients receiving CDK4/6i in first- vs second-line across all measures, despite differences in toxicity rates. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (NCT03425838; https://www.clinicaltrials.gov/study/nct03425838).