Thyroid Cancer, Thyroiditis and Dietary Iodine: A Review Based on the Salta, Argentina Model

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 with other types of thyroid follicular or C-cell derived carcinomas regardless of iodine intake.