Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  HER2-positive Breast Cancer Patients provided written informed consent 2. Postmenopausal or premenopausal or perimenopausal women aged 18-75 years: 1. ≥60 years, or bilateral ovariectomy was previously performed, or 2. <60 years, natural postmenopausal status (defined as a continuous period of at least 12 months following spontaneous cessation without other pathological or physiological causes), estrogen (E2) and follicle-stimulating hormone (FSH) are present at postmenopausal levels 3. Premenopausal or perimenopausal women, willing to receive luteinizing hormone (LHRH) stimulation during the study 3. Histologically or cytologically confirmed HR-positive (ER/PR≥10%), HER2-positive (IHC 3+ or ISH+) breast cancer 4. At least one measurable non-visceral metastatic lesion (liver, lung, pleura, pericardium, peritoneum, kidney, adrenal, brain or leptomeningeal metastases are excluded), HR-positive (ER/PR≥10%), HER2-positive (IHC 3+ or ISH+), (≥10 mm on T1-weighted, gadolinium-enhanced MRI) (RECIST v1.1) 5. Previous treatment with HER2 inhibitors to be discontinued prior to first study treatment administration (at least 14 days for trastuzumab and other antibodies, at least 7 days for lapatinib) 6. Previous chemotherapy, biological or target therapy to recurrent or metastatic disease are not allowed; Previous radiotherapy allowed, but radiotherapy must have been discontinued at least 14 days prior to first study treatment administration. 7. Eastern Cooperative Oncology Group (ECOG) performance score of 0 to 2 8. Life expectancy > 24 weeks 9. left ventricular ejection fraction (LVEF) of 50% or higher at baseline (within 42 days before randomization) 10. Previous adjuvant chemotherapy treatment is allowed 11. Previous adjuvant trastuzumab treatment is allowed 12. Hormone therapy must have been discontinued at least 1 month prior to recruitment 13. Patients with good compliance 14. Patients must have recovered to baseline condition or to Common Terminology for Adverse Events (CTCAE) version 5.0 grade = 1 from any acute CTCAE v. 5.0 grade =2 side effects of previous treatments 15. Without infection of human immunodeficiency virus (HIV) on central laboratory assay results prior to randomization 16. Alanine aminotransferase (ALT) </= 2.5 × the upper limit of normal (ULN), Aspartate aminotransferase (AST) </= 2.5 × ULN prior to randomization 17. Total bilirubin (TBIL) </= 1.25 × ULN 18. Alkaline phosphatase (ALK) </= 2.5 × ULN 19. Gamma glutamyl transpeptidase (GGT) </= 2.5 × ULN 20. Serum total bilirubin (TBil) </= 1.5 × ULN 21. Serum creatinine (Scr) </= 1.5 × ULN 22. WBC >/= 3×109/L, Blood neutrophil count >/= 1×109/L, Platelet count >/= 100×109/L, HB >/= 9 g/dL 23. Albumin >/= 30g/L 24. Women of child-bearing age who had a negative serum pregnancy test (within 14 days before randomization) should take effective contraceptive measures  Primary and metastatic lesion lack of histological or cytological confirmation of HR-positive (ER/PR≥10%), HER2-positive (IHC 3+ or ISH+) 2. Breast cancer with visceral metastases (liver, lung, pleura, pericardium, peritoneum, kidney, adrenal, brain or leptomeningeal metastases) 3. Inflammatory breast cancer 4. Having a life-threatening metastatic visceral disease, defined as extensive liver damage or brain or leptomeninges damage (past or present) or symptomatic pulmonary lymphatic diffusion. Patients with discrete pulmonary parenchyma metastasis were eligible if the investigators determined that their respiratory function was not significantly impaired by the disease. 5. Disease progression or recurrence within 12 months after neo/adjuvant endocrine therapy 6. Unable to tolerate endocrine therapy, including those who with symptoms, who have spread to the viscera, and who are at risk for short-term life-threatening complications (including uncontrolled thorax, pericardium, or abdominal cavity exudation, pulmonary lymphangitis, and more than 50% liver damage). 7. CT or MRI confirmed the presence of brain or leptomeningeal metastases. 8. Any other current malignancy or malignancy diagnosed within the past five years (other than breast cancer, carcinoma in situ of the cervix, skin basal cell carcinoma or squamous cell carcinoma), unless radical treatment is performed and there is no evidence of recurrence or metastasis within the last 5 years. 9. Non visceral metastatic lesions cannot be evaluated by v1.1 10. Active infection with human immunodeficiency virus (HIV) prior to first study treatment administration. 11. History of participating any other clinical trials within 30 days prior to randomization 12. Known hypersensitivity (Grade 3 or 4) to Pertuzumab, Trastuzumab, Fulvestrant or Capecitabine or the excipients of any of the trial drugs 13. Pregnancy or lactation 14. Uncontrolled illnesses including symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia requiring therapy, myocardial infarction within the past 6 months, or active infection 15. severe pulmonary and renal disease 16. Patients with GI tract disease resulting in an inability to take oral medication, malabsorption syndrome, a requirement for IV alimentation, prior surgical procedures affecting absorption, uncontrolled inflammatory GI disease (e.g., Crohn's, ulcerative colitis) 17. Legal incompetence or limitation. 18. Considered unable to complete the study or sign the informed consent due to a medical or mental disorder by the investigator