Puma Biotechnology Presents Data from the Phase III ExteNET Trial in Early Stage HER2-Positive Breast Cancer Patients at the Virtual 2021 ASCO Annual Meeting

Puma Biotechnology, Inc. (NASDAQ: PBYI), a biopharmaceutical company, presented results from the Phase III ExteNET trial assessing the impact of neratinib treatment duration on overall survival (OS) in patients with early stage HER2-positive breast cancer at the virtual 2021 ASCO Annual Meeting. The presentation, entitled “Association between treatment duration and overall survival in early-stage HER2+ breast cancer patients receiving extended adjuvant therapy with neratinib in the ExteNET trial,” is included in the Breast Cancer—Local/Regional/Adjuvant Poster Session (#540).

ExteNET was a multicenter, randomized, double-blind, Phase III trial of 2,840 HER2-positive early stage breast cancer patients who received neratinib after neoadjuvant and/or adjuvant therapy with chemotherapy and trastuzumab-based treatment. Patients were randomly assigned to one year of treatment with either oral neratinib 240 mg/day or placebo.

The poster presented by Professor Beverly Moy summarizes descriptive analyses evaluating the impact of duration of neratinib on clinical outcomes including invasive disease-free survival (iDFS) and distant disease-free survival (DDFS) at 5 years, and overall survival (OS). The analyses were performed in the intention-to-treat (ITT) population and subgroups of clinical interest including the HR+/≤1 year population (patients with hormone receptor-positive (HR+) disease who initiated neratinib within 1 year after prior trastuzumab) and within that subgroup, in the no pathologic complete response (pCR) group (patients from the HR+/≤1-year population with residual disease post-neoadjuvant therapy). Efficacy outcomes in patients who completed neratinib therapy were compared with placebo (all randomized patients). Completion of therapy was defined as patients who were on treatment for ≥ 11 months. Patients who ended neratinib therapy because of disease recurrence before 11 months were also considered with those who ‘completed therapy’ to reduce guarantee-time bias.

Among patients who completed ≥ 11 months of neratinib therapy, OS (median follow-up of 8.0 years) was improved versus placebo in each of the 3 groups. In the intention-to-treat (ITT) population, 872 of 1420 patients (61.4%) in the neratinib arm completed ≥ 11 months of treatment; OS rates were 92.2% vs 90.2% in the neratinib vs placebo arms, respectively, corresponding to a 2.0% improvement (HR 0.78; 95% confidence interval (CI) 0.58-1.04). In the HR+/≤1 year patient population, 402 of 670 patients (60%) in the neratinib arm completed ≥ 11 months of treatment; OS rates were 95.2% vs 89.4% in the neratinib vs placebo arms, respectively, corresponding to a 5.8% improvement (HR 0.49; 95% CI 0.29‒0.78). In the HR+/ <1 year, no pCR group, 92 of 131 patients (70.2%) in the neratinib group completed ≥ 11 months of treatment; OS rates were 95.4% vs 82.2% in the neratinib vs placebo arm, respectively, corresponding to a 13.2% improvement (HR 0.29; 95% CI 0.10–0.68).