SONIA Trial (CDK4/6i Timing Analysis)

Background

Phase III randomized trial. N=1050 (524 first-line CDK4/6i, 526 second-line CDK4/6i) with HR+/HER2- advanced breast cancer, treatment-naive. Median age 64; >80% postmenopausal. Tests optimal sequencing/timing of CDK4/6 inhibition.

Interventions and follow up

Arm A: Aromatase inhibitor + CDK4/6i (first-line) → fulvestrant (second-line)
Arm B: Aromatase inhibitor (first-line) → fulvestrant + CDK4/6i (second-line)
Primary endpoint: PFS after 2 lines of therapy (PFS2)
mFollow up: 58.5mo

Results

OS (overall, prespecified): 47.9 vs 48.1mo, HR 0.91, 95% CI 0.77–1.07, P=.24 — NS
OS (premenopausal subgroup): HR 0.53, 95% CI 0.32–0.87, favoring first-line CDK4/6i
Sequencing: first-line CDK4/6i did not improve PFS2/OS over deferral in the overall population

Adverse events

Overall burden: first-line CDK4/6i had substantially more total grade 3–4 events (3400 vs 2242) and longer cumulative CDK4/6i exposure
Hematologic: neutropenia and anemia predominant

Conclusions

First-line CDK4/6i did not improve OS vs second-line use in the overall population but increased toxicity and cost. A subgroup signal suggests OS benefit in premenopausal patients with first-line use, informing individualized timing.

Key Limitations

Premenopausal OS benefit is a post hoc subgroup (not prespecified), limiting causal inference; predominantly postmenopausal population (>80%); ~84% of patients discontinuing second line followed similar treatment patterns; increased toxicity with first-line use impacts QoL.

Clinical Context

SONIA supports considering deferral of CDK4/6i to second-line in postmenopausal women, while suggesting first-line benefit in premenopausal patients. Informs ASCO/ESMO discussions on personalized sequencing by menopausal status, toxicity tolerance, and cost.

References