Thyroid Cancer, Thyroiditis and Dietary Iodine: A Review Based on the Salta, Argentina Model
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Thyroid Cancer, Thyroiditis and Dietary Iodine: A Review Based on the Salta, Argentina Model H. Rubén Harach & Gustavo A. Ceballos
Published online: 12 August 2008 # Humana Press Inc. 2008
Abstract Factors that should be considered when studying the effect of dietary iodine in the development of thyroid cancer include pathological criteria, diagnostic techniques, screening programs, radioactive fallout, and standard of medical care in the studied population. In most surveys, papillary carcinoma forms the largest group of thyroid malignancies, both before and after iodine prophylaxis where an increase in the papillary:follicular carcinoma ratio is also noted. Undifferentiated carcinomas decrease after salt prophylaxis. In Salta, Argentina, the increasing incidence of clinically significant papillary thyroid cancer and the decrease of undifferentiated carcinoma after iodine prophylaxis are probably due to better access to health centers and consequent earlier detection of differentiated precursor tumors. Autoimmune focal and diffuse or Hashimoto’s thyroiditis are linked to dietary iodine. Pathological studies made in different regions indicate that these types of thyroiditis occur more frequently in areas of iodine sufficiency than in areas of iodine deficiency, and increase after iodine prophylaxis both in non-goitrous and iodine-deficient areas like Salta, Argentina. An increase of lymphocytic thyroiditis could be linked to an increased incidence of primary thyroid lymphoma, and thyroiditis is more commonly associated with papillary carcinoma than
H. R. Harach (*) Servicio de Patología, Hospital “Dr. A. Oñativia”, E. Paz Chain 36, 4400 Salta, Argentina e-mail: [email protected] H. R. Harach : G. A. Ceballos Pathology Unit and Service of Surgery, “Dr. A. Oñativia” Hospital, Salta, Argentina
with other types of thyroid follicular or C-cell derived carcinomas regardless of iodine intake. Keywords thyroid cancer . thyroiditis . iodine . endemic goiter
Introduction There are many problems in assessing possible changes in thyroid cancer incidence rates in relation to iodine intake. Factors such as standard of medical care, pathological techniques, screening programs, radioactive fallout, population age, etc., may show significant variations with time particularly in endemic goiter regions before and after iodine prophylaxis [1]. Other important factors that should also be taken into account include the virtual incorporation of clinically non-significant papillary microcarcinomas found on thyroidectomy specimens, either incidentally or by preoperative ultrasound-guided fine needle aspiration cytology [2], as well as the pathological criteria used for classifying thyroid cancer, particularly for the differentiation between follicular adenoma, follicular carcinoma, and the follicular variant of papillary carcinoma [3, 4]. High or low iodine intake can lead to other clinical and morphological reactions involving the thyroid gland. As far as morphology is concerned, iodine deficiency is related to the development of
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