This is a a multicenter Phase II clinical study investigating efficacy of pyrotinib combined with dalpiciclib combined with letrozole in ER-positive and HER2-positive advanced breast cancer patients. The sample size is 63.

This is a a multicenter Phase II clinical study investigating efficacy of pyrotinib combined with dalpiciclib combined with letrozole in ER-positive and HER2-positive advanced breast cancer patients. Patients receive pyrotinib 320mg/d, dalpiciclib 125mg/d, d1-21, q28d. One cycle is 28d.

Inclusion Criteria:

1. The subjects voluntarily joined the study, signed the informed consent, and had good compliance
2. Postmenopausal or premenopausal/perimenopausal women aged ≥18 years and ≤75 years
3. Patients with recurrent/metastatic breast cancer confirmed by histopathology with positive ER expression and positive HER2 expression
4. Have at least one extracranial measurable lesion that meets RECIST 1.1 criteria
5. At most one previous trastuzumab containing systemic therapy for recurrent metastatic breast cancer

Exclusion Criteria:

1. Subjects had untreated central nervous system metastasis
2. Bilateral breast cancer, inflammatory breast cancer, or latent breast cancer
3. Previous treatment with any CDK4/6 inhibitors
4. Inability to swallow, intestinal obstruction, or other factors affecting drug use and absorption
5. Subject has had other malignancies (except cured basal cell carcinoma of the skin and carcinoma in situ of the cervix) within 5 years or at the same time