Geographical correlation between incidence of benign disease and that of cancer of the thyroid among the population of the Rhône-Alpes Région of France.

Objective: To analyze, at a population level, the relation between the incidences of benign thyroid diseases in patients submitted to surgery and that of thyroid cancers based on their respective geographical distributions. Methods: The study included 3169 cases (691 cancers and 2478 benign diseases) operated on in 2002 in the Rhone-Alpes region, which is subdivided into eight departements and 311 cantons. Results: The total thyroid intervention rate was 54.6/100 000 (23.4 and 86.4), and the annual cancer incidence was 11.9/100 000 (4.7 and 13.8) for men and women respectively. The prevalence of cancer among thyroid surgery was 21.8% and that of cancer discovered in goiters increased with age (44% at 60 years). Intervention rates varied from department to departement. In women, the incidence of microcancers was correlated to the thyroid intervention for benign pathologies rate. In men, the incidence of supracentimetric cancers was related to the TIBR. At the canton level, the relative risk of benign diseases was correlated to that of cancers. TIBR and incidence of cancers were higher in urban cantons than in nonurban ones. The density of endocrinologists influenced the prevalence of cancers among all the cases submitted to surgery. Conclusion: In the Rhone-Alpes population with high rates of thyroid cancer incidence and of thyroid surgery, a number of correlations were found according to gender and tumor size. However, the general incidence of cancer was not directly related to surgical activity. Geographical variability may be related to the heterogeneous medical and pathological practices.