[Undifferentiated carcinomas of the thyroid corpus. Apropos of 10 cases]

Ten undifferentiated thyroid carcinomas detected between 1976 and 1991, were reviewed by means of immunohistochemical techniques. These tumors were highly aggressive with a mean survival rate of three months after the histological diagnosis. They were predominant in women and always occurred in old people (mean age 63.1 years). Four tumours were composed of differentiated trabecular areas. Another one was included in a microvesicular adenoma and a sixth one occurred as a recurrence of a papillary carcinoma surgically treated four months previously. Six tumours were cytokeratin-positive and two of them showed a cytokeratin-vimentin coexpression. These results, like those of an electron microscopic analysis of 1 case, confirm the epithelial origin of these tumours. Undifferentiated carcinomas must be distinguished from poorly differentiated carcinomas and from malignant non Hodgkin lymphomas which have a better prognosis and a different therapeutic approach. The immunohistochemistry and the electron microscopy are useful to identify undifferentiated thyroid carcinomas.