Clear-cell carcinomas of thyroid gland: a clinicopathological study of 13 cases.

Thirteen primary thyroid clear-cell carcinomas and eight thyroid metastases of renal carcinomas are described. A broad variety of features is shown to be responsible for this follicle cell phenotype, some of which also occur in renal carcinomas. In biopsy specimens these two conditions can only be distinguished by immunohistochemistry. Clinical follow-up disclosed that in the papillary and follicular categories of thyroid cancer the biological behaviour of clear-cell tumours exhibits no significant difference to their non clear-cell counterparts. In the case of eight follicle cell carcinomas, various samples were available for study. These revealed some striking variations in histology at different stages, and even during the same stage, of disease. Both reversal of clear cell change and transitions towards other kinds of metaplasia occurred. Morever, maintenance of follicle cell function was documented in several of these lesions by estimations of serum thyroglobulin levels and radioiodine scans. On the basis of these findings the concept of regarding the clear-cell variant as a distinct subtype of thyroid cancer is refuted. Previous statements on the causal mechanism of clear-cell change are discussed and it is suggested that metaplastic transformation accounts for this phenomenon in at least some instances of this heterogeneous condition.