Inclusion Criteria:

          1. Patients with breast cancer that is confirmed histologically or cytologically

          2. Patients who are confirmed to be HER2 positive for the primary or a metastatic lesion
             at a participating medical institution

          3. Patients with no medical history of treatment for advanced/recurrent cancer using a
             regimen of drugs including chemotherapeutics

          4. >=6 months have passed since perioperative treatment with anticancer agents

          5. Presence of a measurable lesion not required

          6. Female aged 20-70 years old at the time of consent acquisition

          7. Baseline left ventricular ejection fraction (LVEF) measured by ECHO or MUGA of >=50%

          8. Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0-1

          9. Patients who have maintained major organ functions, meeting all of the following
             criteria on a test within 28 days before enrollment. If there are multiple test
             results during this period, that obtained immediately before enrollment should be
             adopted.

        (1) Neutrophil count: >=1,500/mm3 (2) Platelet count: >=100,000/mm 3 (3) Hemoglobin: >=9.0
        g/dL (4) Total bilirubin: <=1.5 mg/dL (5) AST (GOT), ALT (GPT): <=2.5 times the ULN (<=5
        times in those with liver metastasis) (6) Serum creatinine: <=1.5 mg/dL 10) Patients with a
        life expectancy of at least 6 months 11) Patient who submits written consent herself after
        receiving sufficient explanation about this study 12) Patients who can undergo QOL
        investigation

        Exclusion Criteria:

          1. Patients planning to undergo radical surgery if they respond to a treatment

          2. Patients who have non-hematological adverse events assessed as Grade >=3 in the Common
             Terminology Criteria for Adverse Events ver. 4.0 in the Japanese JCOG version (CTCAE
             v4.0-JCOG) at the time of enrollment

          3. Patients who have symptomatic metastases to the central nervous system or whose
             symptoms are hard to control

          4. Patients who have active double cancer

          5. Patients who have poorly controlled hypertension, or unstable angina

          6. Patients who have a past history of congestive heart failure assessed as Class ll or
             higher in the New York Heart Association (NYHA) classification, or clinically
             significant arrhythmia requiring treatment

          7. Patients with a past history of myocardial infarction within 6 months before
             enrollment

          8. Patients who are expected to undergo major surgical treatment or who had severe injury
             within 28 days before enrollment, or who require major surgical treatment during the
             study treatment period

          9. Patients with interstitial pneumonia which is symptomatic or requires treatment

         10. Pregnant women, those with a positive pregnancy test, and lactating women

         11. Patients with active systemic infection (including HCV and HBV), or who are found to
             be HIV-positive

         12. Patients with hypersensitivity against pertuzumab and trastuzumab

         13. Patients whom the investigator consider unable or unwilling to follow the protocol
             requirements