Unlike early stage breast cancer, metastatic breast cancer (MBC) is generally 
considered incurable except for a small number of patients with oligometastatic 
disease. The goal of treatment of MBC should be the prolongation of life and 
improvement of symptoms and quality of life. The prognoses of patients with MBC, 
however, have been improved with the introduction of newer, more effective 
agents. Therefore, the clinical question arises whether MBC patients can be 
cured with these new therapeutic agents. However, there are a couple of problems 
in tackling this question, including the duration of follow-up and the presence 
of strong adjuvant therapy. Firstly, most trials in MBC have a relatively short 
follow-up; long-term surveillance (>3-5 years) is exceptional, so little is 
known about the definitive outcome and the exact proportion of long-term 
survivors. Secondly, most of the patients have received pre- or postoperative 
adjuvant therapy. The cancer cells at metastatic sites are considered to be 
relatively resistant to the agents used in metastatic settings. Promisingly, a 
number of novel therapeutic agents including antibody-drug conjugates, 
irreversible small molecule HER2-tyrosine inhibitors, and HER2 dimerization 
inhibitors show promise in the treatment of HER2-overexpressing MBC, as well as 
PARP-1 [poly(ADP-ribose) polymerase-1] inhibitors for triple-negative breast 
cancer.