 Pyrotinib is an oral tyrosine kinase inhibitor targeting both HER-1 and HER-2 receptors. This study is a randomized, multi-center, multinational, open-label, active-controlled, parallel design study of the combination of pyrotinib plus capecitabine versus the combination of lapatinib plus capecitabine in HER2 MBC patients who have prior received anthracyclin, taxane or trastuzumab. Patients will be stratified by weather have prior use of trastuzumab and randomized in a 1:1 ratio to one of the following treatment arms: 