Clinical outcome of patients with childhood acute lymphoblastic leukaemia and an initial leukaemic blood blast count of less than 1000 per microliter

Background: One of the strongest predictive factors for therapy outcome in childhood acute lymphoblastic leukaemia (ALL), treated according to ALL-BFM protocols, is the response to initial prednisone treatment. Prednisone response is characterized by the peripheral leukaemic blast count. The threshold value for the characterisation as good or poor prednisone response is 1000 blasts/μl on day eight of initial prednisone treatment. It is frequently being discussed, whether patients with ALL that initially present with < 1000 blasts/μl and still show < 1000 blasts/μl by day eight of treatment, have the same therapy outcome as prednisone good-responders with initially ≥ 1000 blasts/μl. Patients and methods: We evaluated all patients included in the ALL-BFM 90 study showing good prednisone response. This group included 660 patients presenting with < 1000 blasts/μl at diagnosis. We compared these patients with the prednisone good-responders that initially presented with ≥ 1000 blasts/μl. In addition we analysed all patients who showed an increasing blast count within the threshold of 1000 blasts/μl by day eight of treatment. Results: Children presenting with ALL and < 1000 blasts/μl at diagnosis showed a small but significantly better outcome than prednisone good-responders with initially > 1000 blasts/μl (5 year pEFS 0.86 vs. 0.81, P value 0.0064). If analyzed by treatment group, no significant differences were found. Patients with < 1000 blasts/μl on day eight of treatment but increasing blast count from diagnosis until day eight did not perform worse. Conclusion: The prognostic value of the prednisone response is not restricted to childhood ALL patients presenting with > 1000 blasts/μl at diagnosis, but retains its strength as a strong predictor of treatment outcome also in patients with < 1000 blasts/μl at diagnosis.