AUTHOR=Wang Nan , Li Lin , Xiong Youyi , Chi Jiangrui , Liu Xinwei , Zhong Chaochao , Wang Fang , Gu Yuanting 

TITLE=Case Report: Significant Efficacy of Pyrotinib in the Treatment of Extensive Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer Cutaneous Metastases: A Report of Five Cases

JOURNAL=Frontiers in Oncology

VOLUME=Volume 11 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2021.729212

DOI=10.3389/fonc.2021.729212

ISSN=2234-943X

ABSTRACT=Background: Breast cancer (BC) is the most common tumor to develop cutaneous metastases (CM). Most BCs with cutaneous metastasis are human epidermal growth factor receptor 2 (HER2) positive subtypes. Although the molecular mechanisms of  breast cancer metastasis to different sites and the corresponding treatment methods are areas of in-depth research, there are few studies on cutaneous metastasis.
Case Presentation: Five HER2-positive BC patients with extensive cutaneous  metastases were treated with a regimen containing pyrotinib, a novel small-molecule tyrosine kinase inhibitor that irreversibly blocks epidermal growth factor receptor (EGFR), HER2, and human epidermal growth factor receptor 4(HER4), then their cutaneous  metastases quickly resolved at an astonishing speed and their condition was well controlled during the follow-up period. 
Conclusions: 	This case series reports the significant therapeutic effect of pyrotinib on cutaneous metastases of HER2-positive BC for the first time. Based on this, we recommend that pyrotinib can be used as a supplement to trastuzumab for HER2-positive BC patients with cutaneous metastases. In addition, we should consider that the pan-inhibitory effect of pyrotinib on EGFR, HER2 and HER4 may provide a dual therapeutic effect against HER2 and mucin 1(MUC1).