Advanced cancer  is not well defined. Doctors diagnose advanced cancer based on several things:

Some people think that if a cancer has spread to other parts of the body (called metastatic), it is the same as advanced cancer. This is not necessarily true. Some cancers maybe widespread but can still be treatable and sometimes curable. An example of this is testicular cancer, leukemias, and many lymphomas. On the other hand, a cancer may not have spread to distant sites and still be considered advanced because there is too much cancer to be removed or it has caused major health problems. An example of this is pancreatic cancer that has grown into surrounding organs.

In many cases, advanced cancer happens after the person has had cancer for some time and treatment is no longer working. In other cases, the cancer has come back (recurrence) in a patient who appeared to be cancer free (in remission) after treatment. But every person is unique and for some the cancer may already be advanced when they find out they have the disease.

Often "advanced cancer" means that it can't be cured. But even if there is no cure, treatment can sometimes shrink the cancer, help relieve symptoms, and allow the person to live longer. Some people can live many years with advanced cancer.