Follicular thyroid carcinoma with rhabdoid phenotype.

The aim of this paper is to highlight the occurrence of an unusual histological variant of follicular carcinoma of the thyroid. Three cases are presented: each of the tumours contained a significant population of rhabdoid cells (accounting for 30–40% of the total tumour content). They were all found in female patients aged 65, 43 and 56 years, who presented with enlarged thyroid glands and were subjected to lobectomies. The tumours contained foci of well-differentiated follicular carcinoma, with areas of capsular and vascular invasion, and an accompanying rhabdoid cell component that merged with the neoplastic follicles. Immunohistochemically, the follicular component was positive with thyroglobulin, but the rhabdoid cells were negative in all three cases. The cytoplasmic aggregates in the rhabdoid cells were strongly positive for epithelial markers and vimentin. Two tumours pursued an aggressive biological course similar to other composite extrarenal rhabdoid tumours. A rhabdoid component accompanying thyroid follicular carcinomas is an adverse prognostic factor.