Immunophenotypic heterogeneity of hyalinizing trabecular tumours of the thyroid.

AIMS: We studied 12 cases of hyalinizing trabecular tumour of the thyroid gland (HTT) with the aim of reviewing the cytological, histological and immunophenotypic features and of investigating the relationships of HTT with other thyroid neoplasms. METHODS AND RESULTS: Eleven patients were female and one male, aged 8-74 years (median 58). Ten cases had a benign behaviour, while two cases were locally aggressive. Of the latter, one developed distant metastases and the other is a recent case. All patients are alive 6-311 months after diagnosis. Cytologically, HTT was characterized by hypercellular smears with aggregates of roundish cells having features of papillary carcinoma (nuclear grooves, vacuoles) and fragments of fibrous tissue. Histologically, prominent nesting, trabecular growth patterns and a hyaline stroma (partly positive for laminin and collagen type IV) were found. One case was associated with a papillary microcarcinoma. Two additional cases had extensive areas of papillary carcinoma. In one of these, hyalinized papillary stalks were observed. All tumours contained thyroglobulin but not calcitonin. High molecular weight cytokeratin (a marker of papillary carcinoma) was focally positive in 4/12 cases only and thyroperoxidase (a marker of follicular adenomas, but not of papillary carcinoma) was found in 3/12 cases. CONCLUSIONS: The immunophenotypic profile and the morphological features suggest that HTTs are an heterogeneous group of tumours, some of them probably representing variants of papillary carcinoma with hyalinized stroma.