Thiopurine S-methyltransferase gene polymorphism and 6-mercaptopurine dose intensity in Indian children with acute lymphoblastic leukemia

The prevalence of thiopurine S-methyltransferase (TPMT) polymorphism and its association with clinical and hematological toxicities was retrospectively analyzed in 71 Indian children with acute lymphoblastic leukemia (ALL). Only heterozygous TPMT alleles were observed (10%, 7/71) with relative frequencies being *1/*3C (4.2%), *1/*2 (4.2%) and *1/*3A (1.4%). The median 6-mercaptopurine dose administered during the maintenance therapy was 31% lower among patients with heterozygous TPMT alleles versus the rest (32.1 mg/m2/day and 46.2 mg/m2/day, p = 0.005), though the myelosuppression and toxicities were similar in both the groups. Identification of TPMT genotype appears to be important in making the ALL treatment more effective and less toxic.