High peripheral blast count in adult acute myelogenous leukemia is a primary risk factor for CNS leukemia.

The lengthening remission duration achievable in acute myelogenous leukemia (AML) places patients at risks for CNS leukemic relapse. We reviewed the data on two Eastern Cooperative Oncology Group (ECOG) trials in acute nonlymphocytic leukemia to determine the incidence of CNS leukemia (CNSL). The incidence of CNSL was 5% (30 of 569 patients) overall, and 3% (ten of 331) in patients in complete remission (CR). A number of factors were evaluated for association with increased risk of CNSL. Men more frequently developed CNSL than women at a three to one ratio, and median presenting WBC counts were higher in affected than unaffected patients (44,200/microL v 17,000/microL, P = .01). The low incidence of CNSL in AML supports the view that CNS prophylaxis is unnecessary. However, because 68% of patients (13 of 19) who developed CNSL early in the course of disease had presenting WBC counts greater than 40,000/microL, screening lumbar punctures should be routinely obtained during induction therapy in patients presenting with high circulating blast cell counts.