This trial is a multicenter, open-label, phase II trial conducted at 23 centers in China. High-risk HER2 positive patients receive pyrotinib 400mg/day for one year or half year for extented adjuvant therapy.

Patients must meet one of the following criteria: N stage ≥1; T stage ≥2; did not achieve pathological complete response (pCR) after neoadjuvant therapy; had pCR after neoadjuvant therapy but with tumor size ≥ 5cm or N stage ≥2; or tumor size less than 2cm but with high Ki67; histologic grade 3 or with lymph node micrometastasis.

Inclusion Criteria:

1. Women aged 18-75 years old
2. HER2 positive breast cancer
3. ECOG PS 0-1
4. Known hormone receptor status
5. Completed 1 year of trastuzumab-based adjuvant therapy within 6 months
6. Patients at high risk

Exclusion Criteria:

1. Serious heart disease or discomfort
2. Inability to swallow, intestinal obstruction, or the presence of other factors that interfere with drug administration and absorption
3. Known allergic history of drug components of this regimen
4. A history of immunodeficiency, including HIV positive, or other acquired, congenital immunodeficiency diseases, or a history of organ transplantation
5. Pregnant and lactating female patients