Thyroid cancer histotype changes as observed in a major general hospital in a 21-year period

The existing registries of thyroid carcinoma are seldom comparable as far as epidemiological data, diagnostic criteria and histopatological description are concerned. Epidemiological studies report a progressive increase in the incidence of thyroid carcinoma in the last twenty years and in both sexes this increase of incidence has been referred to papillary histotype. Data collected from surgical series show a rate of thyroid carcinomas from 7 to 20% of total thyroid surgeries. The present study was designed in order to obtain a retrospective review of the distribution of thyroid carcinoma's different histotypes in the last 21 years in a major General Hospital. Detailed analysis of patients with histologically confirmed thyroid carcinoma admitted between 1974 and 1994 to the Surgery Department of Mauriziano Hospital of Torino, Italy showed an overall 11.8% prevalence of thyroid cancer out of the total thyroid surgeries. The rate of papillary carcinoma was the highest (54.3%) followed by follicular carcinoma (27.6%), anaplastic carcinoma (11.1%), medullary carcinoma (4.6%) and others (2.4%). The papillary-to-follicular ratio varied from 0.60 in 1974-76 to 6.88 in 1992-94. Female to male ratio of all thyroid carcinoma histotypes was 2.0 or more; papillary and follicular histotypes had the highest ratio. The variations of the histotype rate observed may be consequence of the silent increase of daily iodine intake throughout the subsequent years, while improved diagnostic tools available and increased experience of the medical staff have probably increased the number on thyroid ablations performed. Our data confirm the changing epidemiology of thyroid carcinoma, reported by international literature.