Abstract PS10-43: Pyrotinib in the treatment of women with advanced HER2 positive breast cancer: A multicenter, prospective, real world study

Backgrounds: Pyrotinib (an irreversible pan-ErbB receptor tyrosine kinase inhibitor) plus capecitabine have been approved for patients with advanced HER2 positive breast cancer in China. However, the efficacy of pyrotinib in patients with different baseline characteristics in the actual clinical practice has not been reported. This study analyzed the anti-tumor activity and toxicity of pyrotinib in real world setting. Methods: Total 36 hospitals in China participated in the real-world study. Patients with histologically confirmed advanced HER2 positive breast cancer were included in the analyses. All patients received pyrotinib-based therapy were given pyrotinib once a day in a 21-day cycle. The primary endpoint was progression-free survival (PFS). Secondary endpoints included adverse events (AE), objective response rate (ORR), disease control rate (DCR), and overall survival (OS). Results: Periodic analysis results were reported in this study. A total of 231 patients (median age: 53 years [26-78]) were enrolled from February 17, 2019 to June 11, 2020. Among them, 156 (67.53%) patients had visceral metastatic lesions and 39 (16.88%) had brain metastases. HR+, HR-, or unknown HR status for primary tumor accounted for 52.82%, 45.45%, 1.73%, respectively. 206 (89.18%) patients were previously administered with anti-HER2 drugs. Among them, 156 patients had received single type of anti-HER2 drug (153 patients with trastuzumab, 3 patients with trastuzumab biosimilar); 50 patients had received trastuzumab and some other drugs (lapatinib, pertuzumab, T-DM1, trastuzumab biosimilar, and antibody-drug conjugate). 88 (65.67%) patients received pyrotinib-based therapy as a second or further line of treatment. 177 (76.62%) patients initiated pyrotinib treatment at 400 mg, 52 (22.51%) patients started with 320 mg, and 2 (0.87%) patients had a starting dose of 160mg. Treatment regimens were pyrotinib plus capecitabine (95/231), pyrotinib combined with other chemotherapy drugs (41/231), pyrotinib combined with anti-HER2 treatments (57/231), and pyrotinib monotherapy (30/231), pyrotinib combined with endocrine therapy, radiotherapy or antiangiogenic drugs (8/231). Among the 134 patients available for efficacy evaluation, 1 (0.75%) patient achieved complete response (CR), 30 (22.39%) patients had partial response (PR), 86 (64.18%) patients achieved stable disease (SD), and 17 (12.69%) patients had progression disease (PD), resulting in an ORR of 23.14% and DCR of 87.31%. Patients received pyrotinib-based therapy as their first, second, and later lines of treatment had a DCR of 82.05%, 90.91%, and 87.27%, respectively. Among patients receiving ≥3 lines treatment, no statistical significance of the DCR was observed, nonetheless, patients received pyrotinib plus capecitabine had a numerically lower DCR than those received pyrotinib combined with other chemotherapy drugs (85% vs. 92.86%, P=0.704). This is an early stage of data analysis, median progression-free survival has not yet been reached. The most common AE was diarrhea (81.68%), but only 16 (7.93%) patients reported Grade ≥ 3 diarrhea which could be well controlled. Other AEs included leukopenia (31.69%), neutropenia (30.69%), anemia (27.23%), increased alanine aminotransferase (15.36%), decreased appetite (11.39%), and stomatitis (6.44%). No treatment-related death occurred. Conclusions: Pyrotinib demonstrated an encouraging efficacy and manageable safety profile in patients with advanced HER2+ breast cancer. More data would be analyzed and reported in the future. Citation Format: Jifeng Feng, Lili Zhang, Zhaoji Guo, Jun Zhou, Mingzhen Zhu, Xiaohong Wu, Tongbo Yi, Yujiang Guo, Xiaoqin Li, Hao Yu, Weidong Mao, Bei Gu, Zhengxiang Han, Yun Zuo, Yanhua Liu, Xufen Wang. Pyrotinib in the treatment of women with advanced HER2 positive breast cancer: A multicenter, prospective, real world study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-43.