title: Toxicity and efficacy of 6-thioguanine versus 6-mercaptopurine in childhood lymphoblastic leukaemia: a randomised trial.
abstract: BACKGROUND
  6-mercaptopurine has been a standard component of long-term continuing treatment for childhood lymphoblastic leukaemia, whereas 6-thioguanine has been mainly used for intensification courses. Since preliminary data have shown that 6-thioguanine is more effective than 6-mercaptopurine, we compared the efficacy and toxicity of the two drugs for childhood lymphoblastic leukaemia.
  
  
  METHODS
  Consecutive children with lymphoblastic leukaemia diagnosed in the UK and Ireland between April, 1997, and June, 2002, were randomly assigned either 6-thioguanine (750 patients) or 6-mercaptopurine (748 patients) during interim maintenance and continuing therapy. All patients received 6-thioguanine during intensification courses. We analysed event-free and overall survival on an intention-to-treat basis. We obtained toxicity data using an adverse-event reporting system, with follow-up questionnaires to seek detailed information for specific toxicities. This trial is registered with the International Standard Randomised Controlled Number 26727615 with the name ALL97.
  
  
  RESULTS
  After a median follow up of 6 years, there was no difference in event-free or overall survival between the two treatment groups. Although 6-thioguanine conferred a significantly lower risk of isolated CNS relapse than did 6-mercaptopurine (odds ratio [OR] 0.53, 95% CI 0.30-0.92, p=0.02), the benefit was offset by an increased risk of death in remission (2.22, 1.20-4.14, p=0.01), mainly due to infections during continuing therapy. Additionally, 95 patients developed veno-occlusive disease of the liver. Of these, 82 were randomly assigned 6-thioguanine, representing 11% of all 6-thioguanine recipients. On long-term follow-up, about 5% of 6-thioguanine recipients have evidence of non-cirrhotic portal hypertension due to periportal liver fibrosis or nodular regenerative hyperplasia.
  
  
  CONCLUSIONS
  Compared with 6-mercaptopurine, 6-thioguanine causes excess toxicity without an overall benefit. 6-mercaptopurine should remain the thiopurine of choice for continuing therapy of childhood lymphoblastic leukaemia.
authors.affiliation: Department of Paediatric Haematology, Sheffield Children's Hospital, Sheffield S10 2TH, UK. ajay.vora@sch.nhs.uk
authors.forename: Ajay
authors.initials: A
authors.lastname: Vora
authors.forename: Chris D
authors.initials: CD
authors.lastname: Mitchell
authors.forename: Lynne
authors.initials: L
authors.lastname: Lennard
authors.forename: T O B
authors.initials: TO
authors.lastname: Eden
authors.forename: Sally E
authors.initials: SE
authors.lastname: Kinsey
authors.forename: John
authors.initials: J
authors.lastname: Lilleyman
authors.forename: Sue M
authors.initials: SM
authors.lastname: Richards
mesh_terms: D000293:Adolescent; D000964:Antimetabolites, Antineoplastic / Q000009:adverse effects / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D008297:Male; D015122:Mercaptopurine / Q000009:adverse effects / Q000627:therapeutic use*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000401:mortality; D013866:Thioguanine / Q000009:adverse effects / Q000627:therapeutic use*
chemical_list: D000964:Antimetabolites, Antineoplastic; D015122:Mercaptopurine; D013866:Thioguanine