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The influence of thiopurine methyltransferase (TPMT) genotype on treatment outcome was investigated in the United Kingdom childhood acute lymphoblastic leukaemia trial ALL2003, a trial in which treatment intensity was adjusted based on minimal residual disease (MRD). TPMT genotype was measured in 2387 patients (76% of trial entrants): 2190 were homozygous wild-type, 189 were heterozygous for low activity TPMT alleles (166 TPMT*1/*3A, 19 TPMT*1/*3C, 3 TPMT*1/*2 and 1 TPMT*1/*9) and 8 were TPMT deficient. In contrast to the preceding trial ALL97, there was no difference in event-free survival (EFS) between the TPMT genotypes. The 5-year EFS for heterozygous TPMT*1/*3A patients was the same in both trials (88%), but for the homozygous wild-type TPMT*1/*1 patients, EFS improved from 80% in ALL97% to 88% in ALL2003. Importantly, the unexplained worse outcome for heterozygous TPMT*1/*3C patients observed in ALL97 (5-year EFS 53%) was not seen in ALL2003 (5-year EFS 94%). In a multivariate Cox regression analysis the only significant factor affecting EFS was MRD status (hazard ratio for high-risk MRD patients 4·22, 95% confidence interval 2·97-5·99, P < 0·0001). In conclusion, refinements in risk stratification and treatment have reduced the influence of TPMT genotype on treatment outcome in a contemporary protocol.

Original publication

DOI

10.1111/bjh.13469

Type

Journal article

Journal

Br J Haematol

Publication Date

08/2015

Volume

170

Pages

550 - 558

Keywords

acute lymphoblastic leukaemia, mercaptopurine, minimal residual disease, thiopurine methyltransferase, Alleles, Child, Child, Preschool, Disease-Free Survival, Female, Follow-Up Studies, Heterozygote, Homozygote, Humans, Infant, Male, Methyltransferases, Neoplasm Proteins, Neoplasm, Residual, Precursor Cell Lymphoblastic Leukemia-Lymphoma, Risk Assessment, Risk Factors, Survival Rate, United Kingdom