OCCULT CARCINOMA OF THE THYROID - A SYSTEMATIC AUTOPSY STUDY FROM SPAIN OF 2 SERIES PERFORMED WITH 2 DIFFERENT METHODS

Background. Occult carcinoma of the thyroid (OCT) seems to be present in a significant proportion of the general population. Previous studie s have shown large variations in the prevalence rate of OCT, which may be due to differences in the prevalence rates between different geogr aphic areas, but also to the lack of standardized diagnostic criteria and methods of examination. The epidemiologic features of OCT at autop sy in Spain are reported for the first time. Methods. To investigate t he influence of methodology in the results, two series were studied, e ach one using a different method. In Series A, 625 cases were studied, and sections were taken only from grossly visible lesions. In Series B, the whole thyroid glands of 100 autopsies were cut into blocks and all blocks were histologically studied. In addition, immunocytochemica l stainings were performed in Series B for calcitonin, thyroglobulin, and epidermal keratin. Results. Series A found 33 OCTs (5.28%), consis ting of 29 occult papillary carcinomas (OPC), 2 occult follicular carc inomas, 1 occult oxyphilic carcinoma, and 1 occult medullary carcinoma . Series B found 22 OPC cases (22%) containing a total of 53 tumor foc i. Tumor diameter varied from 0.07 to 1.8 mm. The epithelial cells of all the OPC were negative for calcitonin, weakly positive for thyroglo bulin, and intensely positive for epidermal keratin. One case had meta stasis in a regional lymph node. Conclusions. This study shows that th e differences in the incidence of OCT found in numerous studies are du e not only to actual different geographic incidences but also to the m ethod of study.