Many so-called solid tumors of childhood—those that do not develop in the blood—are often staged by a system that classifies the disease by whether it can be completely removed surgically. The involvement of lymph nodes and spread to distant sites are also considered. Greatly simplified, Stage I usually refers to local disease that can be entirely removed by a surgeon. Stage II could still be a local disease that may also be removed but has extended beyond the immediate area of the tumor. Stage III disease tends to be more extensive but localized in one particular region of the body, and Stage IV disease is widespread, having spread though the blood or lymphatic system to produce new tumors (metastases) in other organs.
Leukemia is often defined according to its potential for relapse as low risk, average risk and high risk. The child with low-risk leukemia has an excellent chance of responding to therapy in the long term and the best chance of being cured. On the other hand, a child with high-risk leukemia needs more intensive treatment to have an equivalent chance of response and cure.
