Abstract OT2-14-01: Pyrotinib after trastuzumab-based adjuvant therapy in high-risk early human epidermal growth factor receptor 2-positive breast cancer: a multicenter phase 2 trial
Authors: Cao Feilin , Ma Zhaosheng , Hu Guinv , Zhu Xiaotao , Li Shuguang , Chen Shuzheng , Chen Binglie , Li Zhanwen , Wu Weizhu , Ji Xiaochun , Shu Jingde , Tao Deyou , Hu Xiaoqing , Zheng Min , Wang Ouchen , Feng Qingjing , Hao Jing , Li Xujun 
Published: March 2023

Objective: Trastuzumab-based adjuvant therapy was demonstrated to improve the prognosis of early human epidermal growth factor receptor 2 (HER-2) positive breast cancer, while about 10% of patients showed primary resistance. ExteNET study showed that 1 year of neratinib, an irreversible pan-HER tyrosine kinase inhibitor, after trastuzumab-based adjuvant therapy significantly improved invasive disease-free survival (iDFS) in women with HER2-positive breast cancer. Besides, for patients with early hormone receptor positive breast cancer within 1 year of prior trastuzumab with residual disease after neoadjuvant therapy, extended adjuvant neratinib showed prolonged overall survival, which suggested the potential benefit of extended adjuvant therapy for high-risk patients. Pyrotinib is an oral irreversible pan-HER receptor tyrosine kinase inhibitor targeting epidermal growth factor receptor, HER2, and HER4, which showed promising efficacy and manageable safety profiles in the treatment of HER-2 positive advanced breast cancer. In this study, we aimed to evaluate the efficacy and safety of extended adjuvant pyrotinib following trastuzumab-based adjuvant therapy in patients with high-risk early HER-2 positive breast cancer.

Methods: In this ongoing multicenter, open-label, phase II trial at 23 centers in China, women with operable high-risk early HER-2 positive breast cancer and known hormone receptor status, who have completed trastuzumab-based adjuvant therapy within 6 months were enrolled. High-risk patients must meet one of the following criteria: N stage ≥1; T stage ≥2; did not achieve pathological complete response (pCR) after neoadjuvant therapy; had pCR after neoadjuvant therapy but with tumor size ≥ 5cm or N stage ≥2; or tumor size less than 2cm but with high Ki67, histologic grade 3 or with lymph node micrometastasis. Eligible patients were assigned to receive 6 month or 1 year of oral pyrotinib 400mg/day. The primary endpoint was the 2-year iDFS rate.

Results: Between January, 2019 and February, 2022, a total of 142 eligible women were enrolled and assigned to receive pyrotinib, with a median age of 50 (range: 25-72) years old. Ninety-seven patients had a T stage ≥2. A total of 108 patients (76.1%) had node-positive disease, and 64 (45.1%) were hormone receptor positive. Twenty-five patients used neoadjuvant therapy previously, and all of them did not receive pCR (Table 1). After a median follow-up of 20 (range: 0.25-41) months, the 2-year iDFS rate was not available. Two and four patients reported invasive disease events after 6-month and 1-year of follow-up, with the 6-month and 1-year iDFS rates of 98.6% and 97.2%, respectively. The most common adverse events reported was diarrhea (78.2%), followed by fatigue (36.6%), lymphocyte count decreased (36.6%), nausea (33.1%) and hand-foot syndrome (33.1%). Forty-three patients experienced grade 3 diarrhea, and no grade 4 or higher adverse event was reported (Table 2). Adverse event leading to treatment discontinuation occurred in 12 (8.5%) patients.

Conclusion: Extended adjuvant pyrotinib administrated after trastuzumab-based adjuvant therapy was well-tolerated and showed potential efficacy in high-risk early HER-2 positive breast cancer. The follow-up is ongoing to determine the long-term benefit of extended adjuvant pyrotinib.

Table 1. Baseline characteristics of patients ER: estrogen receptor; PR: progesterone receptor.

Table 2. Treatment-emergent adverse event occurring in at least 10% of the patients

Citation Format: Feilin Cao, Zhaosheng Ma, Guinv Hu, Xiaotao Zhu, Shuguang Li, Shuzheng Chen, Binglie Chen, Zhanwen Li, Weizhu Wu, Xiaochun Ji, Jingde Shu, Deyou Tao, Xiaoqing Hu, Min Zheng, Ouchen Wang, Qingjing Feng, Jing Hao, Xujun Li. Pyrotinib after trastuzumab-based adjuvant therapy in high-risk early human epidermal growth factor receptor 2-positive breast cancer: a multicenter phase 2 trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-14-01.