IMMUNOPHENOTYPIC HETEROGENEITY OF HYALINIZING TRABECULAR TUMORS OF THE THYROID

Aims: We studied 12 cases of hyalinizing trabecular tumour of the thyr oid gland (HTT) with the aim of reviewing the cytological, histologica l and immunophenotypic features and of investigating the relationships of Ha with other thyroid neoplasms. Methods and results: Eleven patie nts were female and one male, aged 8-74 years (median 58). Ten cases h ad a benign behaviour, while two cases were locally aggressive. Of the latter, one developed distant metastases and the other is a recent ca se. All patients are alive 6-311 months after diagnosis. Cytologically , HTT was characterized by hypercellular smears with aggregates of rou ndish cells having features of papillary carcinoma (nuclear grooves, v acuoles) and fragments of fibrous tissue. Histologically prominent nes ting, trabecular growth patterns and a hyaline stroma (partly positive for laminin and collagen type TV) were found. One case was associated with a papillary microcarcinoma. Two additional cases had extensive a reas of papillary carcinoma. In one of these, hyalinized papillary sta lks were observed. All tumours contained thyroglobulin but not calcito nin. High molecular weight cytokeratin (a marker of papillary carcinom a) was focally positive in 4/12 cases only and thyroperoxidase (a mark er of follicular adenomas, but not of papillary carcinoma) was found i n 3/12 cases. Conclusions: The immunophenotypic profile and the morpho logical features suggest that HTTs are an heterogeneous group of tumou rs, some of them probably representing variants of papillary carcinoma with hyalinized stroma.