Variable. Stage 4 metastatic breast cancer can be controlled with chemotherapy in some. Some can live years depending on the individual's response to chemotherapy treatments. Others will not do as well, and each person is different. Discuss in more detail with the treating medical oncologist who can give better answers, knowing the patient and the specific details of the breast cancer.
Survival. It depends upon what type of breast cancer it is er/pr positive? Her2 status and the sites of mets whether bones alone or organs like liver lungs brain etc. On an average women with stage 4 breast cancer are surviving 3-4 years with diagnosis, some longer than that some not.