The nature of remission in acute myeloblastic leukaemia.

15 patients with acute myeloblastic leukaemia (AML) in remission were given immunotherapy and 17 similar patients were given immunotherapy plus chemotherapy with the drugs used to induce remission. Median remission length was 245 days for both groups and median survival was 465 days for patients given chemoimmunotherapy and 476 days for patients given only immunotherapy. The failure of remission chemotherapy in AML cannot be attributed to induced resistance because the same drugs induced a second remission in 60% of the patients. From laboratory studies with human AML cells it is suggested that in AML the residual leukaemic cells mature after induction chemotherapy and are then refractory to further drug treatment. Relapse occurs when the leukaemic population proliferates and the environment permits dedifferentiation into frank blast cells.