title: Proliferative activity of human thyroid cells in various age groups and its correlation with the risk of thyroid cancer after radiation exposure.
abstract: BACKGROUND
  The thyroid gland is vulnerable to the carcinogenic effects of ionizing radiation, and there is a well-documented inverse correlation between thyroid cancer and age at exposure, particularly for ages less than 20 yr. One of the factors responsible for this phenomenon may be more rapid cell proliferation in children.
  
  
  OBJECTIVE
  The objective of this study was to determine the proliferative rate of normal human thyroid cells in different age groups.
  
  
  METHODS
  We used immunohistochemical analysis to determine the Ki-67 proliferative index in 117 thyroid glands obtained at autopsy, including 25 fetal thyroids (11-40 wk gestation), 55 childhood thyroids (0-19 yr), and 37 adult thyroids (20-60 yr).
  
  
  RESULTS
  The rate of Ki-67 labeling in the three groups was 7.4 +/- 6.10, 0.23 +/- 0.15, and 0.08 +/- 0.04% respectively, demonstrating an overall trend for diminishing proliferative activity of thyroid cells with increasing age. However, a lack of correlation was noted between the slopes of cancer risk calculated from previous studies of irradiated populations and proliferative rate in the pediatric age intervals of 0-4 and 5-9 yr, suggesting that other factors are likely to be responsible for the particularly high sensitivity to radiation-induced thyroid cancer among the youngest children.
  
  
  CONCLUSIONS
  Our findings of a general decrease in proliferative activity of thyroid cells with age may explain, at least in part, the higher risks of radiation-related thyroid cancer in children compared with adults. However, the variation in the rate of cell proliferation is unlikely to be responsible entirely for this phenomenon and other factors may also be involved.
authors: Department of Pathology, University of Cincinnati, 231 Albert Sabin Way, P.O. Box 670529, Cincinnati, Ohio 45267-0529, USA.
authors: Ali G
authors: AG
authors: Saad
authors: Seena
authors: S
authors: Kumar
authors: Elaine
authors: E
authors: Ron
authors: Jay H
authors: JH
authors: Lubin
authors: Jerzy
authors: J
authors: Stanek
authors: Kevin E
authors: KE
authors: Bove
authors: Yuri E
authors: YE
authors: Nikiforov