Thiopurine methyltransferase (TPM T) activity exhibits monogenic co-dominant inheritance, with ethnic differences in the frequency of occurrence of variant alleles. With conventional thiopurine doses, homozygous TPMT-deficient patients (~1 in 178 to 1 in 3,736 individuals with two nonfunctional TPMT alleles) experience severe myelosuppression, 30–60% of individuals who are heterozygotes (~3–14% of the population) show moderate toxicity, and homozygous wildtype individuals (~86–97% of the population) show lower active thioguanine nucleolides and less myelosuppression. We provide dosing recommendations (updates at http://www.pharmgkb.org) for azathioprine, mercaptopurine (MP), and thioguanine based on TPMT genotype.

The Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for Thiopurine Methyltransferase Genotype and Thiopurine Dosing was originally published in March 2011. We reviewed recent literature and concluded that although relevant new evidence has been generated, none of the evidence would change the primary dosing recommendations in the original guideline; therefore, the original publication remains clinically current. Up‐to‐date information on thiopurine methyltransferase (TPMT) gene alleles and nomenclature can be found at PharmGKB (http://www.pharmgkb.org). Clinical Pharmacology & Therapeutics (2013); 93 4, 324–325. doi:

We analyzed the long-term outcome of 1011 patients treated in five successive clinical trials (Total Therapy Studies 11, 12, 13A, 13B and 14) between 1984 and 1999. The event-free survival improved significantly (p=0.003) from the first two trials conducted in the 1980s to the three more recent trials conducted in the 1990s. Approximately 75% of patients treated in the 1980s and 80% in the 1990s were cured. Early intensive triple intrathecal therapy, together with more effective systemic therapy, including consolidation and reinduction treatment (Studies 13A and 13B) as well as dexamethasone (Study 13A), resulted in a very low rate of isolated central-nervous-system relapse rate (<2%), despite the reduced use of cranial irradiation. Factors consistently associated with treatment outcome were age, leukocyte count, immunophenotype, DNA index, and minimal residual disease level after remission induction treatment. Because of concerns about therapy-related secondary myeloid leukemia and brain tumors, in our current trials we reserve the use of etoposide for patients with refractory or relapsed leukemia undergoing hematopoietic stem cell transplantation, and cranial irradiation for those with CNS relapse. The next main challenge is to further increase cure rates while improving quality of life for all patients.

The influence of genetic polymorphism in inosine triphosphate pyrophosphatase (ITPA) on thiopurine-induced adverse events has not been investigated in the context of combination chemotherapy for acute lymphoblastic leukemia (ALL). This study investigated the effects of a common ITPA variant allele (rs41320251) on mercaptopurine metabolism and toxicity during treatment of children with ALL. Significantly higher concentrations of methyl mercaptopurine nucleotides were found in patients with the nonfunctional ITPA allele. Moreover, there was a significantly higher probability of severe febrile neutropenia in patients with a variant ITPA allele among patients whose dose of mercaptopurine had been adjusted for TPMT genotype. In a cohort of patients whose mercaptopurine dose was not adjusted for TPMT phenotype, the TPMT genotype had a greater effect than the ITPA genotype. In conclusion, genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of severe febrile neutropenia, after combination chemotherapy for ALL in which mercaptopurine doses are individualized on the basis of TPMT genotype.

To assess the clinical heterogeneity among patients with acute lymphoblastic leukemia (ALL) and various 11q23 abnormalities, we analyzed data on 497 infants, children and young adults treated between 1983 and 1995 by 11 cooperative groups and single institutions. The substantial sample size allowed separate analyses according to age younger or older than 12 months for the various cytogenetic subsets. Infants with t(4;11) ALL had an especially dismal prognosis when their disease was characterized by a poor early response to prednisone (P = 0.0005 for overall comparison; 5-year event-free survival (EFS), 0 vs 237 712% s.e. for those with good response), or age less than 3 months (P = 0.0003, 5-year EFS, 57 75% vs 23.47 74% for those over 3 months). A poor prednisone response also appeared to confer a worse outcome for older children with t(4;11) ALL. Hematopoietic stem cell transplantation failed to improve outcome in either age group. Among patients with t(11;19) ALL, those with a T-lineage immunophenotype, who were all over 1 year of age, had a better outcome than patients over 1 year of age with B-lineage ALL (overall comparison, P = 0.065; 5-year EFS, 887 713 vs 46714%). In the heterogeneous subgroup with del(11)(q23), National Cancer Institute-Rome risk criteria based on age and leukocyte count had prognostic significance (P = 0.04 for overall comparison; 5-year EFS, 647 78% (high risk) vs 837 76% (standard risk)). This study illustrates the marked clinical heterogeneity among and within subgroups of infants or older children with ALL and specific 11q23 abnormalities, and identifies patients at particularly high risk of failure who may benefit from innovative therapy.

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To determine the clinical significance of minimal residual disease (MRD) in patients with prognostically relevant subtypes of childhood acute lymphoblastic leukemia (ALL), we analyzed data from 488 patients treated in St. Jude Total Therapy Study XV with treatment intensity based mainly on MRD levels measured during remission induction. MRD levels on day 19 predicted treatment outcome for patients with hyperdiploid >50 ALL, NCI standard-risk B-ALL or T-cell ALL, while MRD levels on day 46 were prognostic for patients with NCI standard-risk or high-risk B-ALL. Patients with t(12;21)/(ETV6-RUNX1) or hyperdiploidy >50 ALL had the best prognosis; those with a negative MRD on day 19 had a particularly low risk of relapse: 1.9% and 3.8%, respectively. Patients with NCI high-risk B-ALL or T-cell ALL had an inferior outcome; even with undetectable MRD on day 46, cumulative risk of relapse was 12.7% and 15.5%, respectively. Among patients with NCI standard-risk B-ALL, the outcome was intermediate overall but was poor if MRD was ≥1% on day ≥19 or MRD was detectable at any level on day 46. Our results indicate that the clinical impact of MRD on treatment outcome in childhood ALL varies considerably according to leukemia subtype and time of measurement.

Minimal residual disease (MRD) is an independent prognostic factor in childhood acute lymphoblastic leukemia (ALL). The most widely applied MRD assays in ALL are flow cytometric identification of leukemia immunophenotypes and polymerase chain reaction (PCR) amplification of antigen-receptor genes. We measured MRD by both assays in 227 patients with childhood B-lineage ALL. Of 1375 samples (736 bone marrow and 639 peripheral blood) examined, MRD was o0.01% in 1200, and X0.01% in 129 by both assays; MRD levels measured by the two methods correlated well. Of the remaining 46 samples, 28 had MRD X0.01% by flow cytometry but o0.01% by PCR. However, PCR (which had a consistent sensitivity of 0.001%) detected leukemic gene rearrangements in 26 of these 28 samples. Conversely, in 18 samples, MRD was X0.01% by PCR but o0.01% by flow cytometry. In nine of these samples, flow cytometry had a sensitivity of 0.001%, and detected aberrant immunophenotypes in eight samples. Therefore, the two most widely used methods for MRD detection in ALL yield concordant results in the vast majority of cases, although the estimated levels of MRD may vary in some. The use of the two methods in tandem ensures MRD monitoring in all patients.