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Year : 2016  |  Volume : 13  |  Issue : 2  |  Page : 71-73

Carcinoma showing thymus like differentiation (CASTLE) - A rare thyroid neoplasm

1 Department of Pathology, Smt. Kashibai Navale Medical College and General Hospital, Narhe, Pune, Maharashtra, India
2 Department of Pathology, Bombay Hospital Institute of Medical Sciences, New Marine Lines, Mumbai, Maharashtra, India

Date of Web Publication1-Jun-2016

Correspondence Address:
Dr. Vinod Raosaheb Patil
Flat No. 31-32, Swati Anusaya Society, Trimuti Chowk, Behind Bharati Vidyapeeth, Dhankawadi, Pune - 411 043, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-0354.168895

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Carcinoma showing thymus like differentiation (CASTLE) is a rare tumor involving soft tissues of the neck and the thyroid gland. It arises from ectopic thymus or remnants of branchial pouches in the neck. It may present as an asymptomatic neck or thyroid mass, which may or may not be invasive. Most cases follow an indolent course and have good prognosis. We report a case of 34-year-old female who presented with hoarseness of voice and mass in the neck. Surgical excision was done. Histopathology and immunohistochemistry (CD5 positivity) revealed carcinoma showing thymus like differentiation (CASTLE). No recurrence was noted after one year of follow-up.

Keywords: Carcinoma showing thymus like differentiation, CASTLE, CD5

How to cite this article:
Patil VR, Patel K, Muzumdar G. Carcinoma showing thymus like differentiation (CASTLE) - A rare thyroid neoplasm. Thyroid Res Pract 2016;13:71-3

How to cite this URL:
Patil VR, Patel K, Muzumdar G. Carcinoma showing thymus like differentiation (CASTLE) - A rare thyroid neoplasm. Thyroid Res Pract [serial online] 2016 [cited 2022 Dec 7];13:71-3. Available from: https://www.thetrp.net/text.asp?2016/13/2/71/168895

  Introduction Top

Carcinoma showing thymus like differentiation (CASTLE) was first described by Miyauchi et al. in 1985.[1] Since then very few cases have been reported. It typically occurs in the soft tissues of the neck or in the thyroid gland. It is commonly seen in adults of age group 40 to 50 years and shows equal sex prediliction.[2],[3],[4] It is generally an indolent tumor with good prognosis.[2] Therefore, it should always be differentiated from other more aggressive neoplasms occuring at the same location like metastatic carcinomas, malignant primary thyroid neoplasms and thymic carcinomas etc.

  Case Report Top

A 34-year-old female presented with episodes of hoarseness of voice of one-month duration. She was apparently alright in between the episodes. Local examination revealed a mass in anterior aspect of neck moving with deglutition. A positron emission tomography (PET) scan revealed no increased uptake anywhere else in the body. Fine needle aspiration cytology (FNAC) of the mass was done outside and reported as papillary carcinoma of thyroid.

Patient was referred to our hospital for further management. Surgical exploration revealed an irregular mass in right paratracheal region infiltrating lower pole of thyroid. Few small shotty lymph nodes were detected along the trachea and right recurrent laryngeal nerve. On examination of the frozen section of the paratracheal mass, a differential diagnosis of metastatic carcinoma and CASTLE was given. This was followed by right hemithyroidectomy and lymph node dissection.

Grossly, right thyroid lobe showed gray white tumor infiltrating the lower pole. Few lymph nodes were also received separately.

Microscopic examination of the paratracheal mass revealed a poorly circumscribed carcinoma with infiltrating borders. It was composed of lobules, sheets, nests and trabeculae of polyhedral and slightly fusiform cells within desmoplastic stroma [Figure 1]a. The cells possessed moderate cytoplasm and large vesicular nuclei with prominent nucleoli. Few mitoses were detected. Squamous differentiation was identified focally [Figure 1]b. Small lymphocytes and fewer plasma cells were present in the nests intermingled with neoplastic cells. The tumor infiltrated the lower pole of thyroid [Figure 1]c. Foci of conventional thyroid carcinoma of either follicular or papillary type were not found. Few lymph nodes also showed metastatic deposits of carcinoma.
Figure 1: (a) Nests, trabeculae and sheets of tumor cells with vesicular nuclei and prominent nucleoli (H and E ×100) (b) Focal squamous differentiation (H and E ×200) (c) Involvement of thyroid gland (H and E ×100)

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On immunohistochemical examination, neoplastic cells expressed pancytokeratin, bcl-2, CD-5 [Figure 2]a and [Figure 2]b and were immunonegative for calcitonin, thyroglobulin and thyroid transcription factor-1 (TTF-1).
Figure 2: Immunopositivity of tumor cells for CD5 and bcl2

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Based on these morphological findings, the location of the tumor, and the results of immunohistochemistry, a diagnosis of CASTLE was made. After the surgery, the symptoms disappeared and no recurrence has been noted after one-year of follow-up.

  Discussion Top

Several rare tumors occurring in the soft tissues of the neck and thyroid gland have morphological appearance similar to the fetal, mature or involuted thymus and thymomas.[1],[5],[6] In 1991, Chan and Rosai divided these tumors into four groups on the basis of their morphologic features: 1) ectopic hamartomatous thymoma, 2) ectopic cervical thymoma, 3) spindle epithelial tumor with thymus-like differentiation (SETTLE) and 4) carcinoma showing thymus like differentiation. CASTLE was originally described by Miyauchi et al. as “intrathyroidal epithelial thymoma” in 1985.[1] It was named as CASTLE by Chan and Rosai in 1991.[1] Since then very few cases have been reported.[7] Recently, this disease has been designated as an independent clinicopathological entity of thyroid gland in the latest edition of the World Health Organization classification of tumors of endocrine organs.[8] It arises from either ectopic thymus or remnants of branchial pouches, which retain the potential to differentiate along the thymic line.[4] It is commonly seen in fourth and fifth decades. There is equal distribution among sexes.[2],[3],[4] For unknown reasons, two third of the cases occur on the left-side of the neck. Most of the tumors are seen near the lower pole of thyroid gland.

As discussed earlier, it is difficult to diagnose CASTLE preoperatively because clinical findings such as, palpation of hard tumors, with poor mobility and frequent tumor extension to adjacent organs are common features in aggressive and advanced thyroid carcinomas. But certain clues help to suspect this disease like - location of tumor in lower part of thyroid gland, lobulated appearance of the tumor on sonography, lack of calcification, lack of foci of other thyroid neoplasms, lack of cellular features on FNAC typical of any thyroid neoplasms and lack of rapid tumor enlargement.

Grossly and histologically, the tumor shows many features of thymic differentiation such as - 1) expansile growth pattern 2) lobulated cut surface 3) thick fibrous septa between tumor nests 4) presence of many lymphocytes and plasma cells with scanty neutrophils 5) oval vesicular nuclei with nucleoli and pale cytoplasm 6) squamoid or spindle-shaped epithelial cells with whorls resembling Hassall corpuscles.

Immunohistochemistry plays an important role in diagnosis. The sensitivity and specificity of CD5 immunostaining, a marker of thymic origin, for diagnosis of CASTLE are 82% and 100%, respectively. But the absence of CD5 staining does not completely ruled out. PANCK and bcl-2 also aid in the diagnosis. The absence of TTF-1, thyroglobulin and calcitonin help to rule out primary thyroid neoplasms.

Tumor extension and nodal metastasis are rather common events in this disease. Curative surgery, including resection of organs to which the tumor has extended and systematic lymph node dissection followed by radiation therapy can prevent locoregional recurrence. Roka et al. showed in their systematic literature review that - node-negative CASTLE had a low risk of recurrence. None of the patients with node-negative tumors have died of the disease. Whereas the 5- and 10-year survival rates for node-positive patients were 76% and 57%, respectively. Similarly, patients without tumor extension to adjacent organs have not died of the disease.[9],[10] Because of the rarity of CASTLE tumors, a definitive treatment strategy remains uncertain.

Owing to its location in the neck and clinical presentation as a mass frequently moving with deglutition, it can be mistaken for other relatively aggressive neoplasms like metastatic carcinomas, primary malignant thyroid neoplasms and thymic carcinomas etc., In our case, it was misdiagnosed outside on FNAC as papillary carcinoma of thyroid. Even, histologically it can resemble lymphoplasmacytic or squamous carcinomas of thymus. The clinical outcome of CASTLE is much better than these neoplasms. Hence precise diagnosis is essential.

  References Top

Miyauchi A, Kuma K, Matsuzuka F, Matsubayashi S, Kobayashi A, Tamai H, et al. Intrathyroidal epithelial thymoma: An entity distinct from squamous cell carcinoma of the thyroid. World J Surg 1985;9:128-35.  Back to cited text no. 1
Chan JK, Rosai J. Tumors of the neck showing thymic or related branchial pouch differentiation: A unifying concept. Hum Pathol 1991;22:349-67.  Back to cited text no. 2
Tai CM, Liang CW, Chang TC. Intrathyroidal thymic carcinoma: A case report. J Formos Med Assoc 2003;102:109-12.  Back to cited text no. 3
Ahuja AT, Chan ES, Allen PW, Lau KY, King W, Metreweli C. Carcinoma showing thymiclike differentiation (CASTLE tumor). AJNR Am J Neuroradiol 1998;19:1225-8.  Back to cited text no. 4
Asa SL, Dardick I, Van Nostrand AW, Bailey DJ, Gullane PJ. Primary thyroid thymoma: A distinct clinicopathologic entity. Hum Pathol 1988;19:1463-7.  Back to cited text no. 5
Kakudo K, Mori I, Tamaoki N, Watanabe K. Carcinoma of possible thymic origin presenting as a thyroid mass: A new subgroup of squamous cell carcinoma of the thyroid. J Surg Oncol 1988;38:187-92.  Back to cited text no. 6
Chen L, Chen X, Zhang H, Feng L, Zhu R. Carcinoma of the thyroid gland showing thymic-like elements: Hypofunctioning nodule accumulating (99m) Tc-MIBI and (18) F-FDG.Hell J Nucl Med 2011;14:190-1.  Back to cited text no. 7
Cheuk W, Chan JK, Dorfman DM, Giordano T. Spindle cell tumour with thymus-like differentiation. In: DeLellis RA, Lloyd RV, Heitz PU, et al., editors. Pathology and Genetics of Tumours of Endocrine Organs. World Health Organization Classification of Tumours. Lyon, France: IARC Press; 2004. p. 96-97.  Back to cited text no. 8
Ito Y, Miyauchi A, Nakamura Y, Miya A, Kobayashi K, Kakudo K. Clinicopathologic significance of intrathyroidal epithelial thymoma/carcinoma showing thymus-like differentiation: A collaborative study with Member Institutes of The Japanese Society of Thyroid Surgery. Am J Clin Pathol 2007;127:230-6.  Back to cited text no. 9
Roka S, Kornek G, Schuller J, Ortmann E, Feichtinger J, Armbruster C. Carcinoma showing thymic-like elements: A rare malignancy of the thyroid gland. Br J Surg 2004;91:142-5.  Back to cited text no. 10


  [Figure 1], [Figure 2]

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