Facteurs de risque des cancers thyroïdiens différenciés du sujet jeune : étude cas_témoins dans l'Est de la France – YOUNG THYR

Unit 605 of INSERM (National Institute of Health and Medical Research) has undertaken an epidemiologic study in the East of France whose objective is to identify the environmental and genetic factors, which independently or in interaction, could contribute to the risk of differentiated thyroid cancer in childhood and in young adulthood. This study was initiated within the framework of an invitation to tender at the end of 2003 jointly by INSERM and the Institut Nationale de Veille Sanitaire (InVS). This study is based on a close collaboration with the French network of cancer registers (FRANCIM). In France, the differentiated thyroid cancer remains a rare pathology but a steady incidence increase has been recorded since the mid1970s. Today, this incidence tends to reach 4000 cases per annum. The improvement of diagnostic detection, the evolution of medical practices, together with the histopathologic reclassification of certain benign tumors into cancer partially explain this increase, but the influence of emergent risk factors is also suggested. However, the lack of knowledge of the majority of the risk factors for this cancer raises uncertainties concerning the origin of this pathology. The epidemiologic studies carried out throughout the world were often of reduced size, because of the relative small number of thyroid cancers, in particular in the young population. Except ionizing radiation exposure during childhood, they failed until now to clearly identify other suspected risk factors, which could be responsible for a greatest number of incident cases. Therefore, although this trend in incidence increase of this cancer has been observed before the Chernobyl powerplant accident, it is often seen as one of the medical consequences related to this accident and due to the lack of epidemiologic data in France, this eventuality cannot be excluded. The determination of the environmental and genetic risk factors for the differentiated thyroid cancer, which includes an evaluation of the impact of the Chernobyl fallout will help to better understand the variations of incidence of this cancer, in order to develop prevention strategies, in particular in formulating if necessary proposals to reduce exposure levels. A case is a person, a man or a woman, who has been born from January 1, 1971, with a diagnosis of a differentiated thyroid cancer carried between 2002 and 2006, whereas it lived in one of the eight areas in the East of France. These areas were the most contaminated areas by the fallout due to the Chernobyl nuclear powerplant accident in April 1986. These areas include Alsace, Burgundy, Champagne-Ardennes, Franche-Comte, Lorraine, Rhone-Alpes, Provence-Alpes-Riviera and Corsica. These criteria were defined to cover our objectives : 1) to include children or teenagers of less than 20 years old at diagnosis for those born after 1986, 2) to include subjects which were less than 15 years old at the time of the accident in April 1986 for those born between 1971 and 1986. Taking into account the number of cases which were recorded by the cancer registers and by the medical information departments, the number of expected cases is around of 1000. Controls are randomly selected from the general population living in the the East areas of France. One control per case is matched by sex, year of birth and by region of residence at the time of the case diagnosis. Cases and controls of the same area are interviewed by use of a detailed questionnaire administered by a same trained interviewer during an in-person interview. The interview includes questions about suspected risk factor, but also about milk and vegetables consumption of local products at the time of Chernobyl accident. During this interview, buccal cell sample are also collected for DNA extraction. Unit 605 obtained all the legal authorizations necessary prior to the data and buccal cell collection. Interviwews has been started since July 2005, first in Champagne-Ardennes and Rhone-Alpes, and were then extended to Lorraine in May 2006. The interviews will begin in Alsace in April 2007. The extension of the study to the other areas is planned for 2007 but depends on the subventions that we will obtain. The complete data collection should be achieved in the first semester of 2009, but the first analyses are awaited at the end of 2008. After its achievement, this project will be pooled with 4 other cas-control studies on the risk factors for differentiated thyroid , carried out on the adult population in Metropolitan France and in the TOM-DOM, and in particular in the Pacific Islands where the strongest incidence rates are observed. These pooled studies will include approximately 2000 cases and 2000 controls, of various ethnic origin and very different ways of life, for who environmental risk factors are suspected to have very variable influences according to various genetic susceptibilities. The pooled data will constitute epidemiologic and genetic data bases on thyroid cancers of powerful interest for deciphering the complex network of interrelationships existing between these various factors. At the more fundamental level, the availability of these bases will be extremely useful to develop new tools for modeling the consequences of exposures on human health