Frequency and morphology of malignant tumours of the thyroid before and after the introduction of iodine-prophylaxis.

Reclassification of malignant goitres surgically removed between 1952-1975 reveals remarkable epidemiological alterations. There is a proportional decrease in undifferentiated carcinoma, which in males also represents an absolute decrease. The decrease is due to a change in maximum incidence from the 5th to the 7th decade. Differentiated carcinomas, especially the papillary tumours, increase. Comparison with findings in Switzerland shows many conformities. Iodine-prophylaxis apparently influences the morphology of thyroid carcinoma, as indicated by the time lag between the introduction of iodine-prophylaxis and the appearance of alterations in incidence. Iodine-prophylaxis, acting in this way, will improve survival rates in thyroid cancer.