France is among the countries showing fastest growth of thyroid cancer (TC) incidence and highest incidence rates in Europe. This study aimed to clarify the temporal and geographical variations of TC in France and to quantify the impact of overdiagnosis.
We obtained TC incidence data in 1986–2015, and mortality data in 1976–2015, for eight French departments covering 8% of the national population, and calculated the age-standardised rates (ASR). We estimated the average annual percent changes (AAPC) of TC incidence, overall and by department and histological subtype. Numbers and proportions of TC cases attributable to overdiagnosis were estimated by department and period, based on the comparison between the shape of the age-specific curves with that observed prior to changes in diagnostic practice.
During 1986–2015, there were 13,557 TC cases aged 15–84 years. Large variations of TC incidence were observed across departments, with the highest ASR and the fastest increase in Isère. Papillary subtype accounted for 82.8% of the cases, and presented an AAPC of 7.0% and 7.6% in women and men, respectively. Anaplastic TC incidence decreased annually 3.0% in women and 0.8% in men. Mortality rates declined consistently for all departments. The absolute number (and proportion) of TC cases attributable to overdiagnosis grew from 1074 (66%) in 1986–1995 to 3830 (72%) in 2006–2015 in women, and varied substantially across departments.
Overdiagnosis plays an important role in the temporal and regional variations of TC incidence in France. Monitoring the time trends and regulating the regional healthcare practice are needed to reduce its impact.
- • Mortality rates of TC and incidence of anaplastic subtype declined in France.
- • Spatiotemporal variability in TC incidence was mainly driven by overdiagnosis.
- • Overdiagnosis varied among age groups, across regions, and over time.
Thyroid cancer incidence rates have been increasing worldwide over the past decades , although mortality rates have remained stable or declined in most countries . France is among the countries showing fastest growth of the disease and highest incidence rates in Europe . Thyroid cancer has now become the third most commonly diagnosed cancer in women in this country . The epidemic of thyroid cancer incidence manifested itself with a large variability in the magnitude of the incidence rates both between countries and, within countries, across regions , as well as with changes in the age-specific curve of incidence. A large variability in the incidence rates has been also observed across regions in France .
The introduction of ultrasonography and other diagnostic practices since around the 1980s, in combination with intensified surveillance activities, has allowed the detection of subclinical papillary lesions known to exist in the thyroid gland and likely contributed substantially to the observed increases in incidence . Overdiagnosis is the detection of thyroid cancers that had they not been found through testing would have been unlikely to cause symptoms or death in a patient’s lifetime. Recent study shows that the estimates of thyroid cancer overdiagnosis reached around 70–80% in France for men and women during 2008–2012 . However, it remains unclear the extent to which overdiagnosis has contributed to the increasing trends and geographical variability of thyroid cancer in France.
The goal of this study is to clarify the epidemiological characteristics of thyroid cancer in France, notably the temporal and geographical variations; and to quantify the impact of overdiagnosis on thyroid cancer incidence across regions and over time using a previously developed method.