The answer depends on the leukemia subtype. Early stage, asymptomatic CLL may be managed by a "watch and wait" approach while an aggressive acute leukemia would generally warrant the employment of systemic cytotoxic chemotherapy.

As far as I know, chemotherapy is the only potentially successful treatment for both acute and chronic leukemias. With chronic leukemias treatment may be withheld for a short period of time to see how fast they are progressing.