Staging is a way of describing where the cancer is located, if or where it has spread, and whether it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the cancer's stage, so staging may not be complete until all of the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis. There are different stage descriptions for different types of cancer.

Unlike most solid tumors, leukemias do not have a formal staging system. Regular blood tests (see Diagnosis [2]) are the main ways to monitor a person's recovery from eosinophilic leukemia, including any symptoms related to the disease and the number of immature cells in the bone marrow.