Genetic studies of childhood acute lymphoblastic leukemia with emphasis on p16, MLL, and ETV6 gene abnormalities: results of St Jude Total Therapy Study XII

Abstract

To determine the frequency and prognostic significance of recently described genetic lesions in pediatric acute lymphoblastic leukemia (ALL), all cases with available leukemic cell samples treated on St Jude Study XII were analyzed by molecular techniques for alterations of the p16, MLL and ETV6 genes. Homozygous p16 deletion was seen in 36 of 155 cases, including 14 of 23 T cell cases, but had no prognostic value. Rearrangement of MLL was seen in nine of 170 cases (5%) and conferred a poor prognosis, with a 5-year EFS estimate of only 11 ± 7%, compared with 74 ± 5% for the germline MLL group (P = 0.0001). By contrast, rearrangement of ETV6 was found in 35 cases (21%) and was significantly associated with a better outcome (5-year EFS estimates: 87 ± 7% vs 64 ± 6%). In a Cox regression model adjusted for age, DNA index, race, leukocyte count, treatment group, and CNS status, ETV6 rearrangement retained independent prognostic significance (two-sided P value 0.012). Thus, in this uniformly treated group of patients, we confirmed the unfavorable prognostic significance of MLL rearrangement and demonstrated the favorable impact of ETV6 rearrangement, suggesting that these factors be added to ALL risk classification schemes.