Breast cancer is the most common malignant tumor in women worldwide, and chemotherapy is still the main method of breast cancer treatment. And for locally advanced breast cancer patients, neoadjuvant chemotherapy can further improve treatment efficacy, improve prognosis and increase the rate of breast conserving surgery. The persistence of a minimal residual disease at distant sites after the treatment of a localized breast cancer is a key parameter for posttreatment survival but cannot be reliably assessed by the current biological or radiological tools. Therefore, the prediction of the chemotherapy efficacy is very important. ctDNA, corresponds to fragmented DNA released into the blood stream by tumor masses, the detection and quantification of circulating tumor DNA (ctDNA) is a very promising tool that can assess tumor burden, response to therapy, and minimal residual disease. In this study, we wil collect breast cancer cases treated with neoadjuvant chemotherapy, draw blood and evaluate the efficacy each time before chemotherapy and after surgery, then measure the concentration of ctDNA in each sample. We will also analyze the demographic data,basic treatment and follow-up data including relapse, metastasis and survival.
