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1/5. Spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid.

    BACKGROUND: Tumors of the so-called intrathyroidal epithelial thymoma type are a rare group of thyroid neoplasm tumors. Of this type of tumor, spindle epithelial tumor with thymus like differentiation (SETTLE) has been reported only 17 times in English literature. methods: An 18-year-old woman was initially seen with a 6-cm left thyroid mass that was resected with a left thyroidectomy. Histopathologic features of the excised left thyroid tumor together with an immunohistochemistry and electron microscopy led us to a diagnosis of SETTLE. RESULTS: Most of the specimen was composed of highly cellular spindle cells that formed intersecting and streaming fascicles. The spindle cells showed both vimentin immunoreactivity and cytokeratin immunoreactivity but no immunoreactivity for thyroglobulin or calcitonin. Electron microscopic examination of the spindle cells demonstrated prominent cytoplasmic tonofilaments, desmosomes, and basal lamina consistent with epithelial cell origin. dna content analysis by flow cytometry revealed dna diploidy. CONCLUSIONS: SETTLE of thyroid gland is an extremely rare entity. A review of the literature reveals that SETTLE has distinctive morphologic features and an immunohistochemical profile.
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2/5. Spindle-cell epithelial thymoma. Fine-structural and tumor lymphocyte observations.

    A fine-structural study of a spindle-cell epithelial thymoma in a patient with pemphigus and autoimmune hemolytic anemia is presented and compared with the few previously described. Because light-microscopic features suggested hemangiopericytoma, critical fine-structural comparisons between spindle-cell epithelial thymoma and hemangiopericytoma are detailed. Based upon groups of tonofilaments with desmosomal insertions, abundant well-formed desmosomes, negligible numbers of pinocytotic vesicles, and an absence of myofilaments and dense bodies, an epithelial origin for this tumor is proposed. Langerhans' cell granules, a new observation in thymoma, were found in cells of probably histiocytic origin. Tumor lymphocyte studies revealed that more than 95% of cells formed E rosettes, 36% formed EAC rosettes, yet none contained surface immunoglobulin. The significance of these observations is discussed.
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3/5. Three subtypes of poroid neoplasia in a single lesion: eccrine poroma, hidroacanthoma simplex, and dermal duct tumor. Histologic, histochemical, and ultrastructural findings.

    A single poroid neoplasm composed of three histologically distinct lesions (hidroacanthomas simplex, eccrine poroma, and dermal duct tumor) is reported. Comparative histologic, histochemical, and electron-microscopic studies revealed that each tumor subtype contained varying proportions of poroid cells, clear cells, and cuticular cells. The major component of all three neoplasms was poroid cells, which, under the electron microscope, were characterized by a few, small, poorly developed desmosomes, and were histochemically characterized by a positive succinic dehydrogenase reaction. The dermal duct tumor was cultured, and showed similar histochemical findings to the in vivo poroid cells. These results suggest that poroid cells play the most important role in the histogenesis of these three neoplasms.
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4/5. Thyroid spindle epithelial tumor with thymus-like differentiation (the "SETTLE" tumor). An immunohistochemical and electron microscopic study.

    An intrathyroid primary epithelial spindle-cell tumor with mucous cysts is described in a 9-year-old child. Histologically, this well-circumscribed tumor exhibited a nodular pattern, a prominent spindle cell component with minimal pleomorphism, and well-differentiated mucinous glands within fibrous bands. The spindle cells demonstrated diffuse immunopositivity for cytokeratin and vimentin. Electron microscopy of tissue sections demonstrated that cells contained bundles of cytoplasmic tonofilaments and numerous desmosomes. The light and electron microscopic features and immunohistochemical profile of this tumor were similar to those of recently described thyroid tumors that have been called "SETTLE" tumors (i.e., spindle epithelial tumor with thymus-like differentiation). These uncommon tumors can be considered intrathyroid thymoblastomas and must be regarded as potentially malignant lesions.
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5/5. Spindle epithelial tumor with thymus-like differentiation: a case report with cytologic, histologic, immunohistologic, and ultrastructural findings.

    Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare and distinctive low-grade neoplasm of thymic or related branchial pouch differentiation. The tumor usually presents in the thyroid or lateral neck of children and adolescents and could mimic spindle-cell carcinoma, synovial sarcoma, or malignant teratoma. We report the clinical, cytologic, histologic, immunohistochemical, and ultrastructural features of a SETTLE present for 10 years in a 15-year-old boy. The fine-needle aspirate, initially interpreted as synovial sarcoma, contained numerous clusters of bland spindle cells, with a few detached sheets of columnar mucous cells in a homogeneous background of dissociated spindle cells. Mitoses, necrosis, and atypia were not present. The excised tumor was a well-circumscribed, white-tan mass, with occasional microcysts. Microscopically, the mass consisted of a lobulated, highly cellular, spindle-cell neoplasm arranged in intersecting, whorled, and storiform fascicles separated by fibrous bands. Entrapped within the fibrous bands were squamous-lined cysts and benign-appearing glands lined by columnar epithelium with goblet cells or ciliated pseudostratified epithelium. Immunohistochemically, the spindle cells showed diffuse reactivity for cytokeratins, smooth muscle actin, muscle-specific actin, and MIC-2, and they were negative for epithelial membrane antigen, calcitonin, and thyroglobulin. Ultrastructurally, numerous perinuclear tonofilaments, some aligned with mature desmosomes, were identified in the spindle cells. Occasional cells showed thin filaments with fusiform dense bodies occupying the peripheral cytoplasm. These findings distinguish SETTLE from ectopic thymoma, synovial sarcoma, medullary carcinoma, and teratoma, and they support a thymic epithelial origin for SETTLE, possibly with myoepithelial differentiation.
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