Currently available standard therapies for HER2 overexpressed metastatic breast cancers (MBC) include treatments with chemotherapy or hormonal therapy, alone or in combination with medications that target HER2 gene, such as Trastuzumab or Pertuzumab. This study will examine the effect of treating HER2 overexpressed MBC with the combination of Trastuzumab plus Pertuzumab, without hormonal or chemotherapy, as a first line treatment. If patients progress on this treatment, they will receive hormonal or chemotherapy in addition to the Trastuzumab plus Pertuzumab treatment. The objective is to see how the overall response rate for this treatment compares to other first line treatments in the same patient population.