Thymic involvement and initial white blood count in childhood acute lymphoblastic leukemia.

From 1970 to 1977, two nonrandomized groups of children with acute lymphoblastic leukemia (ALL) were treated with two different induction regimens. A total of 168 patients (group DAL) received induction therapy closely adapted to St. Jude protocol VII. A total of 119 patients (group BFM) were treated with the West Berlin induction protocol. Evaluable for analysis were 138 patients of group DAL and 113 patients of group BFM. Thirty children had thymic involvement (Thy+), 15 in each group. In children without thymic involvement (Thy+), the median initial white blood count (WBC) was 8400/mm3 in group DAL and 8000/mm3 in group BFM. In contrast, the initial WBC was 42,000/mm3 and 79,200/mm3 in the corresponding group with thymic involvement (Thy+). The probability of continuous complete remission (CCR) at 9 years is 0.41 +/- 0.05 for patients without thymic involvement and 0.09 +/- 0.09 for patients with thymic involvement in group DAL, and 0.65 +/- 0.05 for those without thymic involvement and 0.52 +/- 0.13 for those who had thymic involvement in group BFM. After adjustment for initial WBC (regression analysis) the presence of thymic involvement was still a predictor of poor outcome in group DAL (p less than 0.001), whereas it was not a predictor of poor response in group BFM. In view of comparable patient composition in both treatment groups, the favorable prognosis in BFM patients has to be related to the mode of induction therapy.