Diffuse sclerosing variant of papillary carcinoma of the thyroid: a histological and immunohistochemical study of three cases.

Three cases of an unusual diffuse sclerosing variant of papillary carcinoma of the thyroid occurring in young adults are reported. The tumour is characterized by diffuse involvement of one or both lobes of the thyroid, marked squamous metaplasia, numerous psammoma bodies, extensive interstitial fibrosis and heavy lymphocytic infiltration with formation of germinal centres. Lymphatic and vascular permeation was found in all three cases. An interesting finding was the presence of irregularly disposed thin bundles of smooth muscle within the fibrous stroma, presumably a result of splaying of the smooth muscle of vessel walls by the sclerotic process. The papillary areas of the tumour stained for thyroglobulin and cytokeratin, while the squamous areas stained strongly for cytokeratin but not for thyroglobulin. The tumours were negative for calcitonin and carcinoembryonic antigen, but showed weak staining for S-100 protein. Numerous S-100 positive Langerhans/interdigitating reticulum cells were scattered within the tumour islands and the lymphoid infiltrate, suggesting an immunological reaction mediated by these antigen-presenting cells.