History and Signalment: The patient, a 31 year old white female, came in August 1998 with a leftsided neck tumor in the location of the thyroid glandula. The tumor mass was removed, 5x3x3cm great, nodular formed with one solid round, 2.5cm great mass with greyish white cutsurface and firm consistency. Histologically I found a spindlecell neoplasia in only few mitotic figures, including residual follicles and surrounded by a firm pseudocapsule of hyalin tissue. The cells were as well positive with immunohistochemistry reactions against epithelial antigen AE1/AE3 and Vimentin, positive with Thyreoglubulin, negative with S-100-Protein, and in only 5% there was a positive reaction found with Ki67.

Contributor's Diagnostic impression: Dedifferentiated malignant spindlecell tumor of the thyroid gland (carcinoma, follicular).

Diagnosis: Thyroid tissue: Favor spindle epithelial tumor with thymus-like differentiation (SETTLE). Comment: We appreciate your sending the materials requested. After careful examination of the tumor, we conclude that the histologic findings are quite consistent with the unusual tumor described several years ago by Harach et al. Am J Surg Pathol 9: 525-30, 1985 as mentioned above. Subsequent reports appeared in the literature through the years. Histologically the tumor is composed of spindle cells of epithelial origin given a storiform pattern and occasional microcysts. Although muccous cells are not detected in the sections from the single block submitted. The tumor is circumscribed and it is surrounded by a poorly formed capsule. Immunohistochemistry shows strong reaction by the cells to vimentin and CK-7. Anitbodies tested for endocrine differentiation were all negative. In general these tumors appeared to have a slow evolution and a relative good prognosis is expected.