Pediatric Oncology Group Study of in vitro clonal growth patterns of leukemic cells in childhood acute nonlymphocytic leukemia as a predictor of induction response.

Previous studies have shown that clonal growth patterns of leukemic cells from adult patients with acute nonlymphocytic leukemia (ANLL) have prognostic significance for achieving complete remission (CR). In order to determine if a similar correlation between clonal growth patterns and response to chemotherapy exists in childhood ANLL, bone marrow cells from 189 children with newly diagnosed ANLL were cultured in agar. After 7 days of incubation, colonies (greater than 50 cells), large clusters (20 to 50 cells), and small clusters (4 to 20 cells) were counted. Cultures were analyzed for frequency of clusters and colonies as well as for size of clusters. Two growth patterns significantly associated with poor prognosis for achieving CR were large-cluster growth and high cluster incidence (defined as greater than 400 clusters/10(5) bone marrow cells). The CR rate for the former was 53% (versus 79% for non-Group 1 patients; P = 0.03); the CR rate for the latter was 46% (versus 81% for non-Group 2 patients; P = 0.004). These findings indicate that clonal growth characteristics of leukemic cells from childhood ANLL patients are significantly correlated with response to induction chemotherapy and are useful in identifying a subset of patients with poor prognosis.