Corrigendum: Effectiveness and Safety of Pyrotinib, and Association of Biomarker With Progression-Free Survival in Patients With HER2-Positive Metastatic Breast Cancer: A Real-World, Multicentre Analysis - Chen, Qitong; Ouyang, Dengjie; Anwar, Munawar; Xie, Ning; Wang, Shouman; Fan, Peizhi; Qian, Liyuan; Chen, Gannong; Zhou, Enxiang; Guo, Lei; Gu, Xiaowen; Ding, Boni; et al. (Frontiers in Oncology, 2021)