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The state of the art of the treatment of leukemia in childhood in the Netherlands is discussed. The consequences of different diagnostic and therapeutic methods are mentioned. Some suggestions for improvement of the results of nation-wide treatment schemes are given.

Methotrexate (MTX) and 6-mercaptopurine (6MP) have been used since 30 years in the maintenance treatment of acute lymphoblastic leukemia (ALL) of childhood. A synergistic effect of this combination was demonstrated in mouse and childhood leukemia. In this article an overview is given of our investigations, concerning the biochemical basis of this synergism. This synergism is caused by a selective inhibition of the purine de novo synthesis in malignant lymphoblasts by MTX, associated with an enhanced intracellular uptake of 6MP. Pharmacokinetic studies of MTX in various schemes of prophylactic central nervous system treatment in ALL are discussed. Treatment with 24-hr infusions of MTX in a dosage of 5 g/m2, as recommended in the new BFM-86/SNWLK ALL VII protocol, seems to be optimal. Pharmacokinetic studies of intravenous 6MP infusions demonstrated a good cerebral fluid penetration. Exploiting the synergistic action of the combination of MTX and 6MP may offer an improvement of the prophylactic central nervous systems treatment in ALL in the future, using intravenous administration of both MTX and 6MP.

Unlabelled: Relapse is the main obstacle on the way to cure in children with acute lymphoblastic leukemia. In a retrospective study the influence of some prognostic factors and the prognosis have been evaluated in children with an isolated bone marrow relapse and an isolated CNS relapse. The median survival in 152 children with an isolated bone marrow relapse was 13.3 months. Favourable prognostic factors were: duration of first complete remission (CR) longer than 24 months, age at diagnosis between 2 and 6 years, initial leucocyte count below 50 X 10(9)/l, re-induction treatment with four drugs and the institution of a second central nervous system (CNS) prophylaxis. The most important prognostic factor was the duration of the first CR. The median survival in 140 children with a CNS relapse was 25 months. Favourable prognostic factors were: duration of first CR more than 24 months, age at diagnosis between 2 and 10 years, initial leucocyte count below 10 X 10(9)/l and a low blast count at the time of diagnosis of CNS relapse. The estimated survival in children with bone marrow relapse as well as in children with CNS relapse is less than 20%., In Conclusion: with current treatment regimens both bone marrow and CNS relapse have a very poor prognosis in children with acute lymphoblastic leukemia.

A survey is given of our present investigations of the pharmacokinetics of 6MP and the effects of the combination of MTX and 6MP on purine and pyrimidine metabolism. Both drugs are used in the oral maintenance therapy of ALL in children. The very low serum-concentrations after oral administration of 6MP and the short serum-half-life-times after intravenous administration point to more efficacy after prolonged intravenous infusion. The penetration of 6MP in the cerebrospinal fluid after intravenous administration could account for (prophylactic) treatment of the CNS in ALL. Pretreatment of leukemic lymphoblasts with MTX results in an increase of intracellular PRPP due to inhibition of purine de novo synthesis. This can be used for an increased incorporation and conversion of 6MP. Thus, increased incorporation and conversion of 6MP can be obtained when 6MP is added to MTX-pretreated leukemic lymphoblasts at that point of time where MTX causes maximal PRPP accumulation. This will result in increased incorporation of 6MP into nucleic acids and thus in enhanced cytotoxicity. Pharmacokinetic and metabolic investigations of 6MP and MTX could lead to a more rational and more effective use of both agents in patients with ALL.

The Dutch Childhood Leukemia Study Group performed a phase III study (Study ALL V) to evaluate the effectiveness of addition of rubidomycin to induction treatment with vincristine, prednisone and L-asparaginase in children (0-15 years) with standard risk acute lymphoblastic leukemia: WBC less than 50.10(9)/l, absence of mediastinal mass and/or cerebromeningeal leukemia. Furthermore, the influence of some initial patient- en disease-characteristics on the outcome was analysed. Between May 1979 and December 1982 240 patients entered into the study and were randomized into 2 groups: group A (n = 122) received induction treatment with vincristine, prednisone and L-asparaginase; group B (n = 118) received induction treatment with vincristine, prednisone, L-asparaginase and rubidomycin. All patients received cranial irradiation (doses adjusted to age) and intrathecal methotrexate, followed by maintenance treatment with 6-mercaptopurine and methotrexate for 5 weeks, alternated with vincristine and prednisone for 2 weeks, up to 24 months. Complete remission rate was 94% in both groups. Event-free survival at 5 years after diagnosis was higher in group B (62% +/- 4.6%) than in group A (54.2% +/- 4.6%) but the difference was not significant. A higher initial WBC, age greater than or equal to 10 years and a positive acid phosphatase reaction of the leukemic cells were unfavorable prognostic factors (p less than 0.01). Sex, FAB-morphology, immunophenotype and place of treatment (center or general hospital) were not significant factors.