Thyroid & parathyroid

Other thyroid carcinoma



Topic Completed: 1 July 2016

Minor changes: 24 September 2020

Copyright: 2003-2021,, Inc.

PubMed Search: SETTLE thyroid

Shuanzeng (Sam) Wei, M.D., Ph.D.
Zubair W. Baloch, M.D., Ph.D.
Page views in 2020: 2,106
Page views in 2021 to date: 1,693
Cite this page: Wei S. SETTLE. website. Accessed September 21st, 2021.
Definition / general
  • Spindle Epithelial Tumor with Thymus-Like Differentiation
  • Rare initially indolent tumor of neck in young patients (4 - 59 years old, median age 18 years), with delayed (after 5 years) metastases to lymph nodes or lungs, indolent even with metastasis (Head Neck 2015;37:746)
Essential features
  • Low grade biphasic tumor with metastatic potential which occurs in young patients
  • Terminology first used in 1991 (Hum Pathol 1991;22:349)
  • Synonym: Thyroid spindle cell tumor with mucinous cysts
Case reports
  • Thyroidectomy, radiotherapy and chemotherapy are effective in cases with unresectable tumor or metastasis
Gross description
  • Circumscribed or infiltrative, lobulated, white / tan cut surface
Microscopic (histologic) description
  • Encapsulated or infiltrative tumor separated by sclerotic stroma
  • Biphasic pattern: spindle cells and epithelial structures (cords, tubules, papillae or glandular formation)
  • Rare monomorphic variant can have spindle cells or glandular only (Histopathology 1998;33:71)
  • No or rare lymphocytes
  • Mitotic activity or focal necrosis are rare
Microscopic (histologic) images

AFIP images

Spindled cells with mesenchymal appearance

Cytology description
  • Tumor with minimal epithelial component was moderately cellular with single and loosely grouped spindle cells in homogeneous metachromatic material resembling amyloid (Diagn Cytopathol 2007;35:113)
Positive stains
Differential diagnosis
  • Synovial sarcoma: translocation t(x;18) (SSX; SS18 / SYT), increased mitotic figures, no / weak cytokeratin staining, no sclerosing stroma, no epithelial component
  • Medullary carcinoma: not biphasic, amyloid+, calcitonin+, chromogranin+
  • Anaplastic carcinoma: pleomorphic spindle cells, increased mitotic figures, necrosis
  • Ectopic thymoma: with TdT+ lymphocytes
  • Malignant teratoma: with other immature tissue
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