[Anaplastic carcinoma of the thyroid]

Anaplastic carcinoma of the thyroid, also called undifferentiated carcinoma, is a rare variety of thyroid carcinoma observed in elderly subjects, usually female. This tumour presents in the form of a cervical mass and is rapidly fatal, usually within several months. Histologically, anaplastic carcinoma consists of a proliferation of spindle and/or giant cells, more rarely squamous cells, rich in cytonuclear abnormalities and mitotic figures with areas of necrosis. Immunohistochemistry confirms the epithelial nature of the proliferation, as tumour cells are generally labelled by low molecular weight cytokeratins; cytokeratin-vimentin coexpression is not rare. Anaplastic carcinoma can occur de novo or secondary to a pre-existing thyroid lesion, particularly well differentiated papillary or follicular carcinoma; in this latter case, study of p53 can be useful to detect the appearance of anaplastic transformation.