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CASE REPORT  
Year : 2016  |  Volume : 33  |  Issue : 1  |  Page : 27-29
Review of the touch preparation cytology of spindle epithelial tumor with thymus-like differentiation


Department of Pathology, College of Medicine, Hanyang University, Seoul, South Korea

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Date of Web Publication2-Feb-2016
 

   Abstract 

We experienced a case of spindle epithelial tumor with thymus-like differentiation (SETTLE) with touch preparation cytology performed during the intraoperative frozen section diagnosis in a 22-year-old woman. The tumor was partially encapsulated by fibrous capsule. It was a highly cellular biphasic tumor characterized by fasciculated spindle cells with streaming pattern and tubulopapillary epithelial component. The tumor cells were positive for cytokeratin, vimentin, c-kit, epithelial membrane antigen (EMA), and thyroid transcription factor-1 (TTF-1). However, the tumor cells were negative for thyroglobulin, calcitonin, CD99, S-100 protein, CD34, smooth muscle actin, HBME-1, and galectin-3. The reviewed touch smears showed tight clusters with high cellularity. Most cellular clusters showed papillary configuration. However, some clusters showed spindle cells with streaming pattern. The spindle tumor cells showed elongated and cigar-shaped nuclei. Although the incidence is very rare, SETLLE should be included in the differential diagnosis when a spindle cell neoplasm is encountered in touch preparation cytology in young patients with a thyroid mass.

Keywords: Cytology; spindle epithelial tumor with thymus-like differentiation (SETTLE); thyroid; touch preparation

How to cite this article:
Yi K, Rehman A, Jang SM, Paik SS. Review of the touch preparation cytology of spindle epithelial tumor with thymus-like differentiation. J Cytol 2016;33:27-9

How to cite this URL:
Yi K, Rehman A, Jang SM, Paik SS. Review of the touch preparation cytology of spindle epithelial tumor with thymus-like differentiation. J Cytol [serial online] 2016 [cited 2018 Aug 19];33:27-9. Available from: http://www.jcytol.org/text.asp?2016/33/1/27/175495



   Introduction Top


Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a malignant tumor of the thyroid gland, which shows thymic or related branchial pouch differentiation. [1] This tumor is believed to be derived from the third or fourth branchial pouch and thymic remnants. [2] SETTLE is regarded as a low-grade malignant neoplasm because of its slow-growing nature and protracted clinical behavior. [1],[2] To the best of our knowledge, there have been 42 published cases of SETTLE till now. The cytologic features of SETTLE have been rarely described in only eight cases. [1],[3],[4],[5],[6],[7],[8],[9] Here we present the cytologic, histologic, and immunohistochemical findings and the review of literature including its differential diagnosis.


   Case Report Top


A 22-year-old woman complained of a bulging neck mass at the primary clinic. She was diagnosed with "papillary carcinoma" on fine-needle aspiration at a local pathology laboratory. She was transferred to our hospital for surgical treatment. The slides of aspiration cytology were not available for review. The ultrasonography demonstrated a well-defined hypoechoic mass, measuring 3.9 × 3.4 cm in the left lobe of the thyroid. The cervical lymph nodes were unremarkable. She underwent operation.

During the process of frozen section diagnosis, the touch preparation cytology was performed. The frozen section slide showed mostly papillary epithelial configuration intermixed with focal spindle cell component. The touch preparation slides showed tight clusters of spindle or ovoid tumor cells with papillary configuration. The frozen section diagnosis was papillary carcinoma. On the histologic examination, the tumor was a highly cellular biphasic tumor characterized by fasciculated spindle cells with streaming pattern and tubulopapillary epithelial structures. The fasciculated spindle cells had scanty cytoplasm and elongated nuclei with indistinct cell borders. The epithelial cells of the tubulopapillary structures showed abundant cytoplasm and round to ovoid nuclei. The tumor cells were positive for cytokeratin, vimentin, c-kit, epithelial membrane antigen (EMA), and thyroid transcription factor-1 (TTF-1). However, the tumor cells were negative for thyroglobulin, calcitonin, CD99, S-100 protein, CD34, smooth muscle actin, HBME-1, and galectin-3. The final diagnosis was SETTLE. After the final diagnosis was made, touch preparation slides were reviewed. The smears showed tight clusters with high cellularity in a bloody background. Most cellular clusters showed papillary configuration. However, some clusters showed spindle cells with scanty cytoplasm and indistinct cell borders. The spindle cells showed elongated and cigar-shaped nuclei with fine chromatin and inconspicuous nucleoli [Figure 1]. No intranuclear cytoplasmic inclusions or nuclear grooves were seen. After the operation, the patient is doing well without any evidence of recurrence or metastasis for 12 months.
Figure 1: (a and b) The smears were highly cellular and showed a biphasic pattern composed of dense groups of spindle cells and intermixed epithelial clusters. The spindle cells revealed scanty cytoplasm and uniform, elongated, or cigar-shaped nuclei. (c) The epithelial cells showed abundant cytoplasm and variable sized oval nuclei with indistinct nucleoli. (d) The tumor showed a biphasic histologic pattern composed of a spindle cell component and a tubulopapillary epithelial cell component. (a: ×100, b: ×200, c: ×400, d: H and E, ×100)

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   Discussion Top


We experienced a touch preparation cytology of SETTLE during the frozen section diagnosis and described the characteristic cytologic features. We searched reports including the cytologic findings of SETTLE in PubMed and found only eight cases in the English literature. [1],[3],[4],[5],[6],[7],[8],[9] All of them were case reports with fine-needle aspiration cytology. No touch preparation cytology of SETTLE was found as such as our case. Most reports have described the cytologic findings of SETTLE as highly cellular smears composed of spindle cells and/or epithelial cells. The previously reported cases, along with their characteristic cytologic findings, are summarized in [Table 1].
Table 1: The cytologic findings of SETTLE described in the literature

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Recently, Recondo et al. [2] reported a case of SETTLE with a comprehensive review of the literature. They summarized the clinical characteristics of all published SETTLE cases. SETTLE predominantly affected children and young adults. Their mean age was 19 years with a range of 2-59 years. Clinically, SETTLE presented as a painless neck mass. Twenty-six percent of the patients developed metastatic disease. SETTLE showed the latency to develop metastasis with a mean time of 10 years.

Grossly, SETTLE usually presents as an encapsulated or partially circumscribed mass with grayish to tan cut surface. Microscopically, SETTLE shows a highly cellular biphasic pattern and is composed of cellular sheets, short fascicles, interlacing bundles or attenuated storiform arrangement of spindle cells, and glandular epithelial component. [1] The nuclei of spindle cells are oval to elongated and characterized by distinct nuclear membrane, inconspicuous nucleoli, and evenly distributed chromatin. The glandular tumor cells show narrow tubular, tubulopapillary, trabecular, or pseudopapillary structures. [5] Immunohistochemically, the tumor cells show immunoreactivity for pan-cytokeratin, smooth muscle actin, c-kit and vimentin, and no immunoreactivity for thyroglobulin, calcitonin, S-100 protein, chromogranin, synaptophysin, CD34, CD99, and TTF-1. [1],[2]

Because SETTLE is a rare tumor and not often considered, the diagnosis is difficult in cytology practice. [4] Only eight reports have described the cytologic features of SETTLE in fine-needle aspiration cytology samples of SETTLE. [1],[3],[4],[5],[6],[7],[8],[9] The cytology shows a highly cellular smear and a biphasic pattern composed of spindle cells and intermixed epithelial cells. As summarized in [Table 1], the main differential diagnoses in cytologic smears of SETTLE are a spindle cell variant of medullary carcinoma (MC) and synovial sarcoma (SS). SETTLE can be misdiagnosed as MC on fine-needle aspiration cytology. [5] The smear of MC shows a mixed population of spindle, plasmacytoid, and epithelioid neoplastic cells. Irregular aggregates of amorphous amyloid substance can be found in the background. The neoplastic cells of MC have an abundant or moderate amount of fine granular cytoplasm. The nuclei show the neuroendocrine features with eccentric location in both epithelioid and spindle tumor cells. [4],[5] SETTLE can also be misdiagnosed as SS on fine-needle aspiration cytology. The cytologic features of SS may be shared by those of SETTLE. However, the cytologic features of SS reveal severe cytological atypia, many mitotic figures, apoptotic bodies, and necrosis. [5]

We described a case of SETTLE of the thyroid gland with touch preparation cytologic findings. Although the incidence is very rare, SETLLE should be included in the differential diagnosis when a spindle cell neoplasm is encountered in touch preparation cytology in young patients with a thyroid mass. The touch preparation cytology during the frozen section diagnosis may be helpful to confirm the diagnosis of thyroid cancer.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Misra RK, Mitra S, Yadav R, Bundela A. Spindle epithelial tumor with thymus-like differentiation: A case report and review of literature. Acta Cytol 2013;57:303-8.   Back to cited text no. 1
    
2.
Recondo G Jr, Busaidy N, Erasmus J, Williams MD, Johnson FM. Spindle epithelial tumor with thymus-like differentiation: A case report and comprehensive review of the literature and treatment options. Head Neck 2014;37:746-54.  Back to cited text no. 2
    
3.
Su L, Beals T, Bernacki EG, Giordano TJ. Spindle epithelial tumor with thymus-like differentiation: A case report with cytologic, histologic, immunohistologic, and ultrastructural findings. Mod Pathol 1997;10:510-4.   Back to cited text no. 3
    
4.
Kloboves-Prevodnik V, Jazbec J, Us-Krasovec M, Lamovec J. Thyroid spindle epithelial tumor with thymus-like differentiation (SETTLE): Is cytopathological diagnosis possible? Diagn Cytopathol 2002;26:314-9.  Back to cited text no. 4
    
5.
Tong GX, Hamele-Bena D, Wei XJ, O'Toole K. Fine-needle aspiration biopsy of monophasic variant of spindle epithelial tumor with thymus-like differentiation of the thyroid: Report of one case and review of the literature. Diagn Cytopathol 2007;35:113-9.  Back to cited text no. 5
    
6.
Kaur J, Srinivasan R, Kakkar N. Fine needle aspiration cytology of a spindle epithelial tumor with thymus-like differentiation (SETTLE) occurring in the thyroid. Cytopathology 2012;23:413-5.  Back to cited text no. 6
    
7.
Bradford CR, Devaney KO, Lee JI. Spindle epithelial tumor with thymus-like differentiation: A case report and review of the literature. Otolaryngol Head Neck Surg 1999;120:603-6.  Back to cited text no. 7
    
8.
Kirby PA, Ellison WA, Thomas PA. Spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid with prominent mitotic activity and focal necrosis. Am J Surg Pathol 1999;23:712-6.  Back to cited text no. 8
    
9.
Erickson ML, Tapia B, Moreno ER, McKee MA, Kowalski DP, Reyes-Múgica M. Early metastasizing spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid. Pediatr Dev Pathol 2005;8: 599-606.  Back to cited text no. 9
    

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Correspondence Address:
Seung Sam Paik
Department of Pathology, College of Medicine, Hanyang University, 222 Wangsimri-ro, Sungdong-ku, Seoul - 133-792
South Korea
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9371.175495

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