At the time of diagnosis, most cancers are staged to determine how far they have spread from their original location. Stage 1 indicates that the disease has not spread outside the organ where it began; at stage 4, it has spread to distant parts of the body.
With the exception of chronic lymphocytic leukemia (CLL) — which behaves more like lymphoma — leukemia is not staged at diagnosis. That’s because it is a disease of the blood, so at the time of diagnosis, it is already circulating throughout the whole body. Instead of staging, we say that the disease is either active or in remission.