The incidence of this cancer has risen significantly over the past 30 years, both in France and worldwide. Improvements in diagnostic practices are considered the main reason for this increase. Furthermore, exposure to ionizing radiation during childhood remains the primary known risk factor for this cancer. The fallout from the Chernobyl nuclear accident has raised significant concerns in France and Europe, and increasing exposure to ionizing radiation from medical or dental sources is a cause for concern.

Frequently Asked Questions

1) Why study the link between thyroid cancer and Chernobyl? / What health lessons can be learned from the Chernobyl accident?

• In the contaminated areas surrounding the plant (contaminated areas of Ukraine, Belarus, and Russia), the most notable public health consequence is the increase in thyroid cancer among children living near the plant. Studies have shown that significant increases in thyroid cancer were observed as early as the first 3 to 4 years following the accident, primarily among those who were children or adolescents at the time of the accident, and particularly among those under the age of 5. Continued monitoring of incidence shows that excess cases continue to be observed among those who were children in 1986 and are now adults. For more information on these studies, see the IRSN website: http://www.irsn.fr/FR/connaissances/Installations_nucleaires/Les-accidents-nucleaires/accident-tchernobyl-1986/2016-Tchernobyl-30ans-apres/Pages/0-Tchernobyl-2016-30ans-apres-Sommaire.aspx

• France was exposed to fallout from the Chernobyl accident, with levels varying from one department to another. However, exposure in France was much lower than in the "contaminated territories," approximately 100 times lower. For more details on the fallout, see the IRSN website: http://www.irsn.fr/FR/connaissances/Installations_nucleaires/Les-accidents-nucleaires/accident-tchernobyl-1986/2016-Tchernobyl-30ans-apres/Pages/0-Tchernobyl-2016-30ans-apres-Sommaire.aspx

If we make the reasonable assumption that there is no exposure threshold below which there are no effects, even very low exposure levels may be associated with an excess of thyroid cancer. However, it is not always possible to detect this excess because it may fall within the margin of uncertainty of the estimated cases. This is why the impact of the Chernobyl accident on the incidence of thyroid cancer in France is virtually impossible to measure.

2) What were the radioactive fallout effects of the Chernobyl accident in France?

All information on the IRSN website: http://www.irsn.fr/FR/connaissances/Installations_nucleaires/Les-accidents-nucleaires/accident-tchernobyl-1986/2016-Tchernobyl-30ans-apres/Pages/0-Tchernobyl-2016-30ans-apres-Sommaire.aspx

3) Epidemiology of thyroid cancer in France

• In France, in 2015: 2,800 new cases of thyroid cancer in men; 7,300 new cases in women; 143 deaths in men; 215 deaths in women

• Thyroid cancer is more common in women (4th most common) than in men (14th most common).

• In France, between 1980 and 2012: The number of new cases increased by 5% per year among men and women; mortality decreased by 1.9% per year among men and by 3.4% per year among women

• In France, between 1989 and 2004, the 10-year net survival rate increased by 7 percentage points: 85% for new cases diagnosed in 1989–1993; 92% for those diagnosed in 1999–2004

4) What are the risk factors for thyroid cancer?

The primary established risk factor for the "papillary" type (accounting for approximately 80% of thyroid cancers) is exposure to ionizing radiation, primarily during childhood (external exposure: X-rays used, for example, in medical radiography—including dental—and CT scans, as well as gamma rays; internal exposure: inhalation of iodine-131 from fallout following accidents or atmospheric nuclear tests, ingestion of iodine-131, for example to treat hyperthyroidism).Increasing exposure to ionizing radiation from medical or dental sources is raising concerns and may help explain the rise in thyroid cancer cases over the past few decades.Iodine deficiency is an established risk factor for "vesicular" thyroid cancer. Other risk factors (nutritional, reproductive, menstrual, hormonal, anthropometric such as obesity) and possibly environmental (chemical pollutants, pesticides, etc.) may also be involved in the development of this cancer. However, their effects have not yet been clearly established. Not all risk factors for thyroid cancer are yet known and are currently the subject of research.

5) How do we explain the increase in the number of cancer cases over the past 30 years?

Exposure to radioactive fallout from Chernobyl may have contributed to this increase, but to such a small extent that it cannot be quantified. Another risk factor that can be cited is increasing exposure to ionizing radiation from medical and dental procedures during childhood. The significance of this factor has not been formally established. However, it is established that diagnostic practices—that is, methods for detecting this cancer—have improved significantly over the past 30 years, and techniques are becoming increasingly precise (creation of increasingly thin sections; improved ultrasound performance; use of fine-needle aspiration, etc.), which allows for the detection of smaller cancers (a few millimeters) at an earlier stage.

6) Estimates of thyroid cancer incidence by department in metropolitan France

Significant disparities in incidence are observed among French departments. For the period 2007–2011, age-standardized incidence rates varied among departments in metropolitan France from 6.6 (Vosges) to 29.6 cases (Deux-Sèvres) per 100,000 women, and from 2.2 (Manche) to 7.7 cases (Isère) per 100,000 men (table - Thyroid cancers, men, 2007–2011)

The estimated metropolitan average incidence of thyroid cancer in France is approximately 5 per 100,000 among men and 14 per 100,000 among women. 90% of French departments fall within the range of 2.8–7.1 (per 100,000) for men and 8.3–21.2 for women (table - Thyroid cancers, women, 2007–2011)

7) How can these geographical disparities be explained? Did the Chernobyl accident have an impact on these findings?

Significant areas of excess incidence are observed in certain departments in the Southeast and along the southwestern coast compared to the metropolitan average. This can be explained primarily by differences in diagnostic and medical practices. The spatial distribution of incidence and its trends do not allow for an obvious link to an environmental risk factor or to the Chernobyl accident.Other risk factors (nutritional, reproductive, menstrual, hormonal, anthropometric such as obesity) and perhaps environmental (chemical pollutants, pesticides, etc.) may also explain the geographic variations. However, these risk factors have not yet been clearly established, and it is difficult to formulate hypotheses based on the observed geographic disparities in incidence. These factors may also operate at a finer scale than the department.

8) What is overdiagnosis?

The term "overdiagnosis" refers to the early diagnosis of cancers that would never have manifested during a person’s lifetime but are detected through screening. These cancers are a public health concern because they most often lead to surgery that can potentially harm a person’s quality of life, as well as to the initiation of treatment on which the person may become dependent for life. Furthermore, overdiagnosis can entail additional costs, since many of these cancers would have remained asymptomatic.

9) Can we estimate the proportion of thyroid cancers attributable to changes in diagnostic practices?

This is a very difficult task. Generally speaking, descriptive studies do not allow us to distinguish between the effects of diagnostic practices and those of potential risk factors (individual or environmental). It would be necessary to reconstruct the individual medical histories of thousands of people with great precision. However, we can make assumptions based on statistical models, particularly regarding the effect of diagnostic practices, which appears to be significant for thyroid cancer. An IARC study [Vaccarella 2015] thus estimated, approximately, that about 60% of thyroid cancers in France are attributable to diagnostic practices.

For more information:

Colonna M, Uhry Z, Guizard AV, Delafosse P, Schvartz C, Belot A, et al; FRANCIM network. Recent trends in incidence, geographical distribution, and survival of papillary thyroid cancer in France. Cancer Epidemiol 2015;39(4):511-8.

Pascal L, Lasalle JL. Estimation of the incidence of thyroid cancer in Corsica – 1998–2006. Saint-Maurice: Institute for Health Surveillance; 2012. 27 p.

Caserio-Schönemann C, Kudjawu Y, Chérié-Challine L, Guillet A, Musset A, Nicolau J et al. Multi-source cancer surveillance system (SMSC). Pilot study on thyroid cancer in the Île-de-France and Nord-Pas-de-Calais regions. Final study report, October 2010. Saint-Maurice: Institute for Public Health Surveillance; 2011. 68 p.

Uhry Z, Remontet L, Grosclaude P, Velten M, Mitton N, Kudjawu Y, Colonna M. Value of hospital data from 2002–2008 for monitoring the incidence of thyroid cancer in France. Saint-Maurice: Institute for Public Health Surveillance; 2011. 25 p.

Rogel A, Colonna M, Uhry Z, Lacour B, Schwartz C, Pascal L, et al. Trends in the incidence of thyroid cancer in metropolitan France—A 25-year review. Saint-Maurice: Institute for Public Health Surveillance; 2011. 55 p.

Colonna M, Bossard N, Guizard AV, Remontet L, Grosclaude P; the FRANCIM network. Descriptive epidemiology of thyroid cancer in France: incidence, mortality, and survival. Ann Endocrinol 2010;71(2):95-101. doi: 10.1016/j.ando.2009.11.006. Epub 2009 Dec 29.

Leux C, Colonna M, Guizard AV, Uhry Z, Velten M, Ganry O, et al; the FRANCIM network. Time trends in the geographic variation of thyroid cancer incidence by tumor size from 1983 to 2000 in France. Rev Epidémiol Santé Publique 2009;57(6):403-10. doi: 10.1016/j.respe.2009.08.008.

Lasalle JL, et al. Evaluation of thyroid cancer incidence in Corsica based on hospital, health insurance, and pathology laboratory data. Period 1998–2001. Saint-Maurice: Institute for Health Surveillance; 2007. 52 p.

Colonna M, Guizard AV, Schvartz C, Velten M, Raverdy N, Molinie F, et al. A time trend analysis of papillary and follicular cancers as a function of tumor size: a study of data from six cancer registries in France (1983–2000). Eur J Cancer 2007;43(5): 891–900. Epub 2007 Feb 7.

Uhry Z, Colonna M, Remontet L, Grosclaude P, Carré N, Couris CM, Velten M. Estimating subnational and national thyroid cancer incidence in France from cancer registry data and the national hospital discharge database. Eur J Epidemiol 2007;22(9):607-14. Epub 2007 Jul 18.

Chérié-Challine L, et al. Health surveillance in France in connection with the Chernobyl accident. Updated report on thyroid cancers and epidemiological studies underway in 2006. Saint-Maurice: Institute for Public Health Surveillance; 2006. 75 p.

Catelinois O, Laurier D, Verger P, Rogel A, Colonna M, Ignasiak M, et al. Uncertainty and sensitivity analysis in the assessment of thyroid cancer risk related to Chernobyl fallout in Eastern France. Risk Anal 2005;25(2):243-52.

Leenhardt L, Grosclaude P, Chérié-Challine L. Recommendations for the establishment of a national epidemiological surveillance system for thyroid cancers. Report and summary of the report, October 2002. Saint-Maurice: Institute for Health Surveillance; 2003. 32 p.

Verger P, Chérié-Challine L, et al. Assessment of the health consequences of the Chernobyl accident in France: epidemiological surveillance system, state of knowledge, evaluation - Summary of the report. Saint-Maurice: Institute for Health Surveillance; 2000. 19 p.