Historically, a combination of pathological assessment (laboratory evaluation using a microscope) and diagnostic imaging has been used to identify the type of cancer and its stage, and then treatment options. Stage indicates how extensive the cancer is and how much it has spread. Staging usually involves determining the size of the primary tumor and evaluating whether it has remained in the tissue in which it started, whether it has invaded other nearby organs or tissues, and whether cancer cells have spread to distant locations in the body. The cancer is then assigned a stage on a predetermined scale of numbers and letters, for example stage I, II, IIIa, IIIb, IV, etc. The higher number and letter combination indicates more extensive involvement. Treatment is selected based on the stage of disease.
However, research has indicated that identifying the stage of disease may not be the most accurate technique for determining how aggressive it is. For example, some early stage diseases may recur or progress after treatment, while some late stage cancers may reach a state of remission (steady state). These findings suggest that there may be factors other than how the cancer looks under a microscope and how far it has spread at the time of diagnosis that may better indicate the likelihood that a given cancer will recur and/or progress.