1. To explore the predictive value of ctDNA in HER2 positive breast cancer neoadjuvant therapy population;
2. To evaluate the prognostic value of ctDNA in HER2 positive breast cancer neoadjuvant therapy population.

This study plans to enroll 50 HER2 positive breast cancer patients in early stage (T2-3, N0-1, M0)/local late stage (T2-3, N2-3, M0 or T4a-c, Nany, M0), collect baseline tumor tissue samples of patients, as well as peripheral blood samples of multiple nodes at baseline, during new adjuvant therapy, after new adjuvant therapy (before surgery), and after surgery, detect the mutation of tumor tissue through 1021 panel, and conduct ctDNA detection of peripheral blood samples based on personalized panel design based on tumor tissue specific mutations, to explore the efficacy prediction and prognostic predictive value of ctDNA in HER2 positive new adjuvant therapy population.

Inclusion Criteria:

1. Women with breast cancer diagnosed clinically and pathologically, aged 18-75 years;
2. ECOG performance score is 0-1;
3. Histologically confirmed as early or locally advanced invasive breast cancer: the diameter of the primary tumor is more than 2 cm, and HER2 is positive (confirmed by IHC or FISH).
4. The patient did not receive any treatment for breast cancer before enrollment;
5. Having lesions measurable according to RECIST 1.1 standards;
6. The subjects voluntarily joined this study, signed an informed consent form, had good compliance, and cooperated with follow-up; 7) Breast cancer patients who plan to use neoadjuvant therapy.

Exclusion criteria

1. Patients with known metastatic or stage IV breast cancer;
2. There are other untreated malignant tumors other than breast cancer;
3. Patients with one or more serious systemic diseases that, in the eyes of researchers, can impair their ability to complete research;
4. According to the researchers' assessment, there may be other factors that could force the subjects to terminate the study midway, such as suffering from other serious illnesses (including mental illnesses) that require concurrent treatment, severe abnormal laboratory test values, family or social factors, which may affect the safety of the subjects or the collection of experimental data.
5. Unable to follow up with the study according to the determined clinical follow-up period;
6. Cannot accept or provide specified efficacy evaluation methods such as CT.
7. Unable to obtain sufficient tumor tissue samples or peripheral blood samples.

Exclusion Criteria:

- 1) Patients with known metastatic or stage IV breast cancer; 2) There are other incurable malignant tumors present; 3) One or more serious systemic diseases that, in the eyes of researchers, can impair the patient's ability to complete the study; 4) According to the researcher's judgment, there are other factors that may cause the subject to be forced to terminate the study midway, such as other serious illnesses (including mental illness) requiring concurrent treatment, severe abnormal laboratory test values, family or social factors, which may affect the safety of the subject or the collection of trial data.

5) Unable to follow the determined clinical follow-up period in conjunction with the study for follow-up; 6) Unable to accept or provide specified efficacy evaluation methods such as CT.

This study plans to enroll 50 women patients with HER2 positive early (T2-3, N0-1, M0)/local late (T2-3, N2-3, M0 or T4a-c, Nany, M0) breast cancer, who can accept new adjuvant treatment, voluntarily sign the informed consent form, timely and sufficiently obtain tumor tissue and peripheral blood samples for testing, and are willing to cooperate with follow-up.