Background
I-SPY2, a standing, multicenter, adaptive phase 2 neoadjuvant trial ongoing in high-risk clinical stage II/III breast cancer, is designed to evaluate multiple, novel experimental agents added to standard chemotherapy for their ability to improve the rate of pathologic complete response (pCR). Experimental therapies are compared against a common control arm. We report efficacy for the tyrosine kinase inhibitor neratinib.
Methods
Eligible women had ≥2.5 cm stage II/III breast cancer, categorized into 8 biomarker subtypes based on HER2, hormone-receptor status (HR), and MammaPrint. Neratinib was evaluated for 10 signatures (prospectively defined subtype combinations), with primary endpoint pCR. MR volume changes inform likelihood of pCR for each patient prior to surgery. Adaptive assignment to experimental arms within disease subtype was based on current Bayesian probabilities of superiority over control. Accrual to experimental arm stop at any time for futility or graduation within a particular signature based on Bayesian predictive probability of success in a confirmatory trial. The maximum sample size in any experimental arm is 120 patients,
Results
With 115 patients and 78 concurrently randomized controls, neratinib graduated in the HER2+/HR− signature, with mean pCR rate 56% (95% PI: 37 to 73%) vs 33% for controls (11 to 54%). Final predictive probability of success, updated when all pathology data were available, was 79%.
Conclusion
Adaptive, multi-armed trials can efficiently identify responding tumor subtypes. Neratinib added to standard therapy is highly likely to improve pCR rates in HER2+/HR2212; breast cancer. Confirmation in I-SPY 3, a phase 3 neoadjuvant registration trial, is planned.