Thymidylate synthase in childhood acute non-lymphoblastic leukemia.

Childhood acute nonlymphoblastic leukemias (ANLL) of untreated patients were analysed for expression of thymidylate synthase (TS) using immunocytochemistry. Only patients who achieved a complete remission were entered into the study (n = 21 patients). Of the 21 ANLL, 11 showed an overexpression of TS. There exists a strong correlation between the expression of TS and the relapse rate (p = 0.029, Fisher's exact test). Only 3 out of 11 cases of TS-negative patients with ANLL relapsed whereas 8 out of 10 TS-positive cases experienced relapses. The relapse-free intervals of the patients with TS-positive leukemic cells were significantly shorter than those of patients with TS-negative leukemic cells (p = 0.025, log rank test). There was a trend for shorter overall survival times of patients with TS-positive leukemic cells compared with patients with TS-negative leukemic cells (p = 0.12).