Proliferative activity of human thyroid cells in various age groups and its correlation with the risk of thyroid cancer after radiation exposure

J Clin Endocrinol Metab. 2006 Jul;91(7):2672-7. doi: 10.1210/jc.2006-0417. Epub 2006 May 2.


Context: 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.

Design: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Adolescent
  • Adult
  • Aging*
  • Cause of Death
  • Cell Division*
  • Child
  • Child, Preschool
  • Female
  • Gestational Age
  • Humans
  • Immunohistochemistry
  • Infant
  • Infant, Newborn
  • Ki-67 Antigen / analysis
  • Kinetics
  • Male
  • Middle Aged
  • Neoplasms, Radiation-Induced* / pathology
  • Risk Factors
  • Thyroid Gland / chemistry
  • Thyroid Gland / embryology
  • Thyroid Gland / pathology*
  • Thyroid Neoplasms / etiology*
  • Thyroid Neoplasms / pathology


  • Ki-67 Antigen