Different kinds of leukemia are treated differently. Some kinds of leukemia are not staged like you're thinking. Are you asking about a particular kind of leukemia?
Chemo can involve pills/liquid, intramuscular injections, subcutaneous injections, injection directly into the spinal fluid, and intravenous (IV, PICC line, Broviac, port.) Again, each kind of leukemia has a different treatment. With chronic forms, there may be no treatment given right away, or just one pill (Gleevec or something like it.) Chemotherapy may be needed at a later stage. CLL and CML are staged.
With acute leukemias, therapy is a whole mix of things from the get go. With acute lymphoblastic leukemia, treatment is long- about 2.5 years for girls and 3.5 years for boys (can be a bit longer or shorter.) Treatment is broken down into phases (generally induction, consolidation, interim maintenance, delayed intensification, and maintenance.) Chemo is given in the hospital for the first week or so, and then most chemo is given outpatient, in the clinic. Patients take oral meds at home (steroids and/or chemo) and receive other chemo in clinic (IV, shots, and through spinal taps.) With some treatment protocols, patients are admitted to the hospital for 3-5 days to get a certain chemotherapy medication. ALL is not staged. ALL has risk levels, which are assigned based on a number of factors (age at diagnosis, white blood cell count at diagnosis, reponse to initial treatment, and cytogenetics.)
With AML, people tend to be in the hospital for quite a while (weeks to months.) Most of the treatment is given in the hospital, but patients may be able to go home in between rounds.
With stem cell transplant/bone marrow transplant, treatment is done first to get the patient into remission (usually with inpatient or outpatient chemo, and steroids.) This may take a couple of weeks or months. Treatment is then continued, outpatient or inpatient, to keep the patient in remission. When it's time for transplant, the patient is admitted about ten days before transplant, for what's called conditioning. Conditioning involves high dose chemotherapy and total body radiation in order to completely destroy the bone marrow (*note- radiation is occasionally NOT used at all for young children undergoing transplant.) Transplant day then happens (it's pretty uneventful, the bone marrow/stem cells are given like a blood transfusion), and the patient remains in the hospital for a while after that (weeks or months.)
Staging, again, depends on the kind of leukemia. And again, not all are staged like that. So you'd have to be more clear about what kind you are referring to.
Work in pediatric oncology. Most of my patients have leukemia (ages infant-22.)