Breast cancer is the most common malignant tumor in women worldwide,and there exist a large part of patients need to receive neoadjuvant chemotherapy(NAC) before the curative surgery.Circulating tumor DNA(ctDNA) is the circulating free DNA in the blood that originates from cancers,and it can be detected by modern technologies in plasma.In this prospective study,investigators aim to observe the correlation between tumor response to neoadjuvant chemotherapy and ctDNA.

Women with node-positive breast cancer are at high risk for recurrence. Neoadjuvant chemotherapy is traditionally for locally advanced disease, converting an inoperable tumor to a resectable one.In the present study, investigators will focus on breast cancer patients whose primary tumors are large or have lymph node metastases and need to receive neoadjuvant chemotherapy from 2018 to 2019. Circulating tumor DNA(ctDNA) will be obtained from peripheral blood,and the blood samples will be taken before the neoadjuvant chemotherapy、during the chemotherapy、 before the surgery and post surgery visit (within 24 hours after surgery) .Investigators will collect tissue samples both from the breast lump biopsy and the curative surgery. Investigators aim to investigate whether circulating tumor DNA is a sensitive marker to monitor the efficacy of neoadjuvant chemotherapy in breast cancer.

Inclusion Criteria:

• Female patients undergoing neoadjuvant chemotherapy
• Age: 18-70 yrs
• Any menopausal status
• Any hormone receptor status
• Invasive breast cancer proven histologically at diagnosis (before neoadjuvant chemotherapy):
• Locally advanced tumor
• Patients who received 6 to 8 cycles of neoadjuvant chemotherapy.

Exclusion Criteria:

• Failed to retain blood sample before NAC
• Lost more than 2 blood samples during NAC

Breast cancer patient receiving NAC in Shandong Cancer hospital