Late stage breast cancer metastasized to the chest cavity and developed pericardial effusion after treatment, a five-year survival rate of about 20% can be achieved. The following drugs need to be applied under the guidance of a doctor. Breast cancer is a common malignant tumor in women, which can be caused by a variety of factors, such as heredity, hormones, gene mutation and so on. With the development of tumor, when the disease develops to the advanced stage, distant metastasis can occur, such as thoracic metastasis, which can lead to pericardial effusion and other symptoms. At this time, in addition to active radiotherapy and chemotherapy to treat primary lesions and metastatic lesions, pericardial puncture can also be used to extract fluid; diuretics such as hydrochlorothiazide and furosemide can be taken for symptomatic treatment. After active treatment, patients with late-stage breast cancer can obtain a five-year survival rate of about 20%, but the purpose of the treatment in this period is to improve the quality of life of the patients. It is suggested that breast cancer patients should consult regular hospitals in time and standardize the treatment under the guidance of doctors.