title: Iodine deficiency and thyroid cancer trends in three regions of Thailand, 1990-2009.
abstract: Iodine deficiency may play a role in thyroid cancer carcinogenesis. Because Thailand has region-specific historical iodine deficiency, it is ideal to evaluate the potential impact of recent national iodine supplementation policies on thyroid cancer incidence trends.
  
  
  
  We examined thyroid cancer trends in Thailand from 1990 to 2009 in three geographically separated populations (Songkhla Province [south], Chiang Mai Province [north], and Khon Kaen Province [northeast]), each with a different historical prevalence of iodine deficiency. We used Joinpoint analysis and age-period-cohort (APC) models to investigate trends in thyroid cancer incidence.
  
  
  
  Pooled incidence of papillary cancers significantly increased (Males APC: 2.0, p<0.05; Females APC: 7.3 [1990-2001, p<0.05], -2.1 [2001-2009]) and incidence of follicular cancers significantly decreased (Males APC: -5.2, p<0.05; Females APC: -4.3 [1990-1998, p<0.05], 12.3 [1998-2001], -17.0 [2001-2005, p<0.05], 8.2 [2005-2009]) in both males and females between 1990 and 2009. The largest increases in papillary cancer incidence, and the largest decreases in follicular cancer incidence, occurred in historically iodine-deficient regions. Interestingly, the significant histological changes coincided with Thailand's most recent national iodination policy. The thyroid cancer trends in females were better explained by period effects than cohort effects.
  
  
  
  This study adds to the research indicating that papillary carcinoma incidence increases, and follicular carcinoma incidence decreases, as population-level iodine deficiency declines, and suggests that iodine exposure may affect late stages of thyroid carcinogenesis. However, our findings are limited by the ecological study design and lack of data prior to iodine supplementation.
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, United States. Electronic address: smitro@email.gwu.edu.
authors.forename: Susanna D
authors.initials: SD
authors.lastname: Mitro
authors.affiliation: Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI, United States. Electronic address: rozekl@umich.edu.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Rozek
authors.affiliation: Department of Otorhinolaryngology, Faculty of Medicine, Khon Kaen University, Thailand. Electronic address: patvat@kku.ac.th.
authors.forename: Patravoot
authors.initials: P
authors.lastname: Vatanasapt
authors.affiliation: Cancer Unit, Srinagarind Hospital, Faculty of Medicine, Khon Kaen University, Thailand. Electronic address: krisuw@kku.ac.th.
authors.forename: Krittika
authors.initials: K
authors.lastname: Suwanrungruang
authors.affiliation: Division of Therapeutic Radiology and Oncology, Department of Radiology, Faculty of Medicine, Chiang Mai University, Thailand. Electronic address: imjai@hotmail.com.
authors.forename: Imjai
authors.initials: I
authors.lastname: Chitapanarux
authors.affiliation: Division of Head, Neck and Breast Surgery, Department of Surgery, Faculty of Medicine, Chiang Mai University, Thailand. Electronic address: ssrisukh@med.cmu.ac.th.
authors.forename: Songpol
authors.initials: S
authors.lastname: Srisukho
authors.affiliation: Epidemiology Unit, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand. Electronic address: hutcha.s@psu.ac.th.
authors.forename: Hutcha
authors.initials: H
authors.lastname: Sriplung
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, United States. Electronic address: rmeza@umich.edu.
authors.forename: Rafael
authors.initials: R
authors.lastname: Meza
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D007455:Iodine / Q000172:deficiency*; D008297:Male; D008875:Middle Aged; D013785:Thailand / Q000453:epidemiology; D013964:Thyroid Neoplasms / Q000453:epidemiology*; D055815:Young Adult
chemical_list: D007455:Iodine
keywords: Epidemiology; Iodine; Thailand; Thyroid neoplasms