Leukemia is mainly treated with combination chemotherapy or stem cell transplantation to achieve complete remission (CR) with disappearance of signs and symptoms of leukemia and normal blood and bone marrow images.
The criteria for CR are:
- No clinical signs of anemia, hemorrhage, infection, or leukemic cell infiltration;
- Blood picture hemoglobin >90g/L, normal or reduced white blood cells, sorted without infantile cells, platelets >100×10/L;
- Bone marrow picture of primitive cells plus early-stage cells (or naive cells) <5%, normal erythrocyte system and megakaryocyte system.
A patient with leukemia who achieves CR is not said to be cured. The number of leukemia cells in the patient’s body at the time of the leukemia diagnosis is about 10, and 10 to 10 residual leukemia cells remain in the body after CR. These residual leukemia cells in the body are called minimal residual disease (MRD).
Currently, the sensitivity of MRD testing is only 10, which means that there are fewer than 10,000 leukemia cells in the body. MRD proliferates slowly and is a major cause of leukemia relapse, and if treatment is stopped immediately after reaching CR status, most patients will relapse within 6 to 18 months; the longer a patient remains in CR, the less likely they are to relapse.
After 5 years of sustained CR in patients with leukemia, the relapse rate is generally less than <1%, at which point it is considered “clinically cured.