spindle epithelial tumor with thymus-like element

Definition: Spindle epithelial tumor with thymus-like elements is a rare thyroid lesion of children and young adults thought to be derived from branchial pouch remnants or foci of ectopic thymus.

Images

 https://twitter.com/juan_rosai/status/657923979949293568

Digital cases

 JRC:2671 : Spindle epithelial tumor with thymus-like element (SETTLE)
 JRC:15042 : Spindle epithelial tumor with thymus-like element (SETTLE) with very florid, yolk-sac like appearance.

The lesion is poorly understood, and although it was originally believed to follow an indolent clinical course, its potential for late metastasis is becoming generally acknowledged.

SETTLE is a low-grade malignancy, with potential for late lung, lymph node, and other visceral metastases. The clinicopathologic features of SETTLE overlap significantly with those of synovial sarcoma.

Synopsis

 Children and young adults
 M > F
 Painless thyroid mass
 Metastases in >50%

• late metastases well-reported

 Lobulated pattern
 Fascicles of spindle cells merging with tubular / glandular structures
 Strong cytokeratin expression in all components

Evolution

 possible local recurrence
 very rare early micrometastasis
 very rare metastatic dissemination occurring years after surgical resection of the primary lesion (16222481)

References

 Spindle Epithelial Tumor With Thymus-like Differentiation: A Morphologic, Immunohistochemical, and Molecular Genetic Study of 11 Cases. Folpe AL, Lloyd RV, Bacchi CE, Rosai J. Am J Surg Pathol. 2009 May 4. PMID: 19417583

 Erickson ML, Tapia B, Moreno ER, McKee MA, Kowalski DP, Reyes-Mugica M. Early metastasizing spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid. Pediatr Dev Pathol. 2005 Sep-Oct;8(5):599-606. PMID: 16222481

 Chan JKC, Rosai J. Tumors of the neck showing thymic or related branchial pouch differentiation: a unifying concept. Hum Pathol 1991;22:349-367

 Chetty R, Goetsch S, Nayler S, Cooper K. Spindle epithelial tumor with thymus-like element (SETTLE): the predominantly monophasic variant. Histopathology 1998;33:71-74.

 Cheuk W, Jacobson AA, Chan JKC. Spindle epithelial tumor with thymus-like differentiation (SETTLE): a distinctive malignant thyroid neoplasm with significant metastatic potential. Mod Pathol 2000;13:1150-1155.

 Folpe AL, Loyd RV, Bacchi CE, Rosai J. Spindle epithelioid cell tumor with thymus-like elements (SETTLE): A morphologic, immunohistochemical and molecular geneticstudy of 13 putative cases Mod Pathol 2008; 21, Suppl 1, 235A. (Abstract).

 Satoh S, Toda S, Narikawa K, Watanabe K, Tsuda K, Kuratomi Y, Sugihara H, Inokuchi A. Spindle epithelial tumor with thymus-like differentiation (SETTLE). Youngest reported patient. Pathol Int 2006;56:563-567.

 Yu A, LiVolsi V. Spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid with neck lymph node metastasis. A case report. Endocr Pathol 2005;16:139-144.

 Kirby PA, Ellison WA, Thomas PA. Spindle epithelial tumor with thymus-like differentiation (SETTLE) of thyroid with prominent mitotic activity and focal necrosis. Am J Surg Pathol 1999;23:712-716.