Differentiated thyroid carcinomas: the relevance of various pathological features for tumour classification and prediction of tumour progress.

In this series of 263 surgically treated cases of thyroid cancer, 12% were finally classified as benign lesions after histopathological review. Difficulty in the assessment of tumour capsule invasion in follicular neoplasms was the most frequent cause of diagnostic error. Squamous metaplasia, clusters of ground glass nuclei and psammoma bodies were found to be the most specific discriminators between papillary and follicular carcinomas. Among papillary carcinomas, tumour diameter above 30 mm, thyroid capsular invasion and regional lymph node metastases were found to be significant prognostic factors according to survival analyses. Of additional practical importance, our results indicate that tumour infiltration in the thyroid capsule should be reported as a marker of early extra-thyroidal extension.