Epidemiology of Thyroid Microcarcinoma Found in Autopsy Series Conducted in Areas of Different Iodine Intake

The prevalence of thyroid microcarcinomas found at autopsies is 100-1000 times higher than in clinical cancer. The epidemiological and histological characteristics of thyroid microcarcinomas in consecutive series of autopsies performed in two areas of different iodine intake were investigated. Iodine deficient (ID) area: n = 222 (M = 109, F = 113), median age: 74-76 years, median iodine excretion (MIE) of nursing home residents from this area: 70 microg/g creatinine. Iodine sufficient (IS) area: n = 221 (M = 132, F = 89), median age: 68 years, MIE: 500 microg/g creatinine. When compared to the IS area, the results obtained in the ID area showed a higher thyroid weight (mean 27.75 g +/- 18.43 g vs. 16.5 g +/- 9.6 g, p < 0.0001) and a larger number of goitrous glands (50/222 vs. 5/221, p < 0.0001). Altogether 21 microcarcinomas were found (4.74%) with no iodine intake- or gender-related difference: ID n = 11 (4.95%), M/F = 8/3; IS n = 10 (4.52%), M/F = 6/4. Microcarcinomas seemed to be more prevalent in the 40-59-year age group. All microcarcinomas were of the papillary type. In conclusion, compared to clinical cancer, thyroid microcarcinomas are characterized by a two-scale higher prevalence, are not related to iodine intake, gender or nodularity, are most exclusively of the papillary type.