Solitary fibrous tumor of the thyroid gland - Report of seven cases

Solitary fibrous tumor is a soft tissue neoplasm initially described in the pleura but subsequently reported in a Wide variety of locations. The clini cal behavior is usually benign, but the existence of aggressive cases has b een documented both in the pleura and in extrapleural sites. In this report clinical and pathologic features of seven solitary fibrous tumors of the t hyroid gland are presented. Patients' ages ranged from 43 to 64 years (mean 52 years), and tumor sizes varied from 2 to 6 cm. Grossly, the tumors were white-tan and well circumscribed. Microscopically, there was a variegated, wavy, storiform, hemangiopericytic or desmoid-like arrangement of spindle cells. Trapped thyroid follicles within the tumor and peripheral jagged tum or infiltration among follicles were common. There was immunohistochemical reactivity for CD34, CD99, and bcl2, and ultrastructural analysis of one tu mor was consistent with a fibroblastic lineage. The differential diagnosis included other benign and malignant mesenchymal tumors of the thyroid, spin dle cell follicular adenoma, Riedel's thyroiditis, the spindle cell, and pa ucicellular variants of anaplastic carcinoma, papillary thyroid carcinoma w ith exuberant nodular fasciitis-like stroma, and the spindle epithelial tum or with thymus-like differentiation. The cumulative data of 13 cases (compr ised of the seven present cases and the six previously reported) suggest a benign clinical behavior for thyroid SFT.