A Birth Cohort Analysis of the Incidence of Papillary Thyroid Cancer in a Context of Endemic Goiter: Algeria, 1993-2013

  • Background: Over the past three decades, the incidence of papillary thyroid cancer (PTC) has increased in many countries, and the reasons for this increase are still debated. An overdiagnosis due to medical practices has been hypothesized, however the effects of environmental risk factors have not been ruled out. The aim of this study was to determine the age-period-cohort (APC) effects on the incidence of PTC in Oran, Algeria.

    Methods: Using population-based data, we conducted APCs modeling to evaluate birth cohort patterns and age, period, and cohort effects on PTC incidence trends between 1993 and 2013.

    Results: The incidence of PTC has continuously increased over the 1993-2013 period. The average annual rate of increase was +10,2% (95% CI : 7,8%-12,7% ; p<0,0001) in women, and +18,5% (95% CI : 9,5%-28,2% ; p<0,0001) in men. The birth cohort age curves showed a continuing increase in incidence with increasing age, starting at age 29 years for women and 55 years in men, with a strong period effect in both sexes (rate ratio for 2006-2010 versus 1995-1999=1,77 in women and 2.7 in men). For both women and men incidence was higher for individuals born in the 1980s. 

    Conclusion: While the strong period effect in both sexes and the early onset of PTC in women compared with men strongly suggest the role of iodine supplementation and medical practices, the birth cohort-related changes in environmental exposures and lifestyle habits may have contributed to the observed increase in PTC during the past two decades in Oran.

 

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