A Study of Pyrotinib Plus Capecitabine Combined With SRT in HER2+ MBC With Brain Metastases

Inclusion Criteria:

1. Age> 18 years old, female
2. KPS≥70
3. HER2-positive breast cancer is confirmed by the pathology laboratory with animmunohistochemical (IHC) score of 3+ and/or 2+ and a positive in situ hybridization (ISH) test (ISH amplification rate ≥ 2.0)
4. Brain metastasis confirmed by MRI, in line with the indications for whole brainradiotherapy
5. At least one measurable brain lesion exists according to the RECIST 1.1 standard
6. Unlimited number of previous chemotherapy lines
7. Have not used capecitabine in the past, or progressed 6 months after capecitabinestopped, or progressed after capecitabine as adjuvant therapy stopped for one year
8. The expected survival period is more than 12 weeks
9. Patients must have adequate organ function, criteria as follows.
10. Blood routine examination：Absolute Neutrophil Count (ANC)≥1.5×109/L；PLT ≥100×109/L； Hb ≥90g/L
11. Blood chemistry test：TBIL ≤1.5 times the upper limit of normal (ULN); ALT andAST≤3 times ULN; For patients with liver metastases, ALT and AST≤5×ULN; BUN andCr≤1×ULN and creatinine clearance ≥50mL/min (CockcroftGault formula);
12. Ultrasonic cardiogram: LVEF≥50%
13. 12-lead ECG: The QT interval (QTcF) corrected by Fridericia's method is < 470 ms
14. Patients with known hormone receptor status
15. Patients need to voluntarily join this study after they fully understand and sign theinformed consent form. Patients need to have good compliance and be willing tocooperate with follow-up.

Exclusion Criteria:

1. Patients with brain metastases with extensive meningeal metastasis
2. Brain metastases within 5 mm of the hippocampus
3. There are many factors that affect the administration and absorption of drugs, forexample: inability to swallow, chronic diarrhea and intestinal obstruction
4. Those who have received chemotherapy, surgical treatment (excluding local puncture) ormolecular targeted therapy within 4 weeks before enrollment; those who have receivedanti-tumor endocrine therapy after the screening period
5. Participated in other drug clinical trials within 4 weeks before enrollment
6. Have used or are currently using HER2 tyrosine kinase inhibitors (lapatinib,niratinib, pyrotinib, etc.)
7. Suffered from other malignant tumors in the past 5 years, excluding cured cervicalcarcinoma in situ, skin basal cell carcinoma or skin squamous cell carcinoma
8. Receive any other anti-tumor therapy at the same time
9. Those who are known to have a history of allergies to the drug; have a history ofimmunodeficiency, including positive HIV tests, HCV, active hepatitis B, or otheracquired or congenital immunodeficiency diseases, or organ transplants history
10. Have ever suffered from any heart disease, including: (1) arrhythmia requiringmedication or clinical significance; (2) myocardial infarction; (3) heart failure; (4)anyone judged by the researcher as unsuitable for participation becase of other heartdiseases in this trial, etc.
11. Female patients during pregnancy and lactation, female patients with fertility and apositive baseline pregnancy test, or female patients of childbearing age who areunwilling to take effective contraceptive measures during the entire trial period
12. According to the judgment of the investigator, there are accompanying diseases thatseriously endanger the safety of the patient or affect the completion of the study (including but not limited to severe hypertension that cannot be controlled by drugs,severe diabetes, active infection, etc.)
13. The patient has not recovered from the toxicity of the previous treatment to grade 0-1 (except for hair loss)
14. Have a clear history of neurological or psychiatric disorders, including epilepsy ordementia
15. Concomitant use of CYP3A4 inhibitors or inducers or drugs that prolong the QT interval
16. Any other circumstances that are not suitable for inclusion in this study (investigator assessment)