Latent thyroid carcinoma in Iceland at autopsy

The annual incidence rate of thyroid carcinoma in Iceland is high, 4.4 pr. 100,000 men, and 11.7 pr. 100,000 women, as published by the Icelandic Cancer Registry for the period 1955-1984. This rate is more than twice that in the other Nordic countries and one of the highest incidence rates reported anywhere. This led us to investigate the prevalence rate of latent thyroid carcinoma in Iceland. We serially sectioned and examined thyroid glands from 201 consecutive forensic autopsies. Altogether, sixteen carcinomas were identified in fourteen glands: fourteen papillary, one follicular and one medullary carcinoma. We conclude that the prevalence rate of latent thyroid carcinoma in each sex does not follow the frequency distribution of clinical disease, being 7.5% in males and 5.1% in females. Comparisons between populations show the same lack of consistency. Further, most, but not all, latent carcinomas of the thyroid gland are of the papillary type. These findings suggest that promoting factors might be of particular importance where incidence and mortality rates are high, but further research is needed into the role of host resistance.