The Impact Of Diagnostic Changes On The Rise In Thyroid Cancer Incidence

Salvatore VACCARELLA, International Agency for Research on Cancer, France

1 Infections and Cancer Epidemiology Group, International Agency for Research on Cancer, Lyon, France
2 Servizio di Epidemiologia e biostatistica, IRCCS Centro di Riferimento Oncologico di Aviano, Aviano, Italy
3 Section of Cancer Surveillance, International Agency for Research on Cancer, Lyon, France

Purpose: Thyroid cancer (TC) incidence is rising in many high-resource countries, but corresponding mortality is constant or declining. Incidence increases appear largely restricted to small papillary TC in young/middle-age individuals. We compared age-specific incidence rates across countries and time periods to estimate the fraction of TC possibly attributable to diagnostic changes and incremented surveillance of the thyroid gland.
Methods: We focused on high-resource countries: the United States, Denmark, Finland, Norway, Sweden, England and Scotland, France, Italy, Australia, Japan, and the Republic of Korea. Before the 1970s, TC incidence in Nordic Countries increased proportionally to the second power of age, consistently with the multistage model. Using this historical observation as reference, we attributed the progressive departure from linearity of the age-curves in each country to an increased detection of asymptomatic disease in young/middle-age individuals. The proportion of cases attributable to diagnostic changes was estimated from the difference between observed rates and those expected using the Nordic reference.
Results: Attributable proportions were higher in countries with largest incidence increases. Diagnostic changes may account for ≥80% of TC cases diagnosed in 2003-2007 in women aged under 80 in the Republic of Korea, ≥80% in the United States, France, Italy, Australia, and approximately 50% in other countries, except Japan (30%). Attributable proportions were consistent across sexes, although increases were smaller and delayed in men.
Conclusions: A large proportion of TC cases diagnosed in high-resource countries are likely to be due to increased detection of asymptomatic TC. This proportion has progressively increased over time and it is likely to grow further in the future. Since there is evidence of harm but not benefit from the intense scrutiny of the thyroid, the possibility of overdiagnosis and overtreatment of TC should be urgently addressed.
Funding source: None.