Thyroid gland
Other carcinoma

Topic Completed: 1 June 2016

Revised: 12 March 2019

Copyright: 2003-2018,, Inc.

PubMed search: CASTLE thyroid

Shuanzeng Wei, M.D., Ph.D.
Zubair W. Baloch, M.D., Ph.D.
Page views in 2018: 2,426
Page views in 2019 to date: 2,251
Cite this page: Wei S, Baloch Z. CASTLE. website. Accessed November 13th, 2019.
Definition / general
  • CArcinoma Showing Thymus-Like differentiation
  • Terminology first used in 1991 (Hum Pathol 1991;22:349)
  • Also known as intrathyroidal (ectopic) thymic carcinoma
Essential features
  • Intrathyroidal (ectopic) thymic carcinoma located at the lower pole of thyroid
  • Also called intrathyroidal thymoma (not commonly used as it confuses as benign)
  • Mean age 48.5 years
  • Commonly involves the lower pole of the thyroid and surrounding soft tissue
Radiology description
  • Nodular masses located in the lower neck between the inferior pole of the thyroid and the upper mediastinum (Br J Radiol 2016;89:20150726)
Prognostic factors
  • Good prognosis, with 5 year and 10 year survival of 90% and 82%; poorer prognosis if nodal metastases or tumor extension to surrounding tissue (Am J Clin Pathol 2007;127:230)
Case reports
  • Total thyroidectomy with neck dissection and radiation
Gross description
  • Well defined, lobulated white / tan mass
Gross images

Images hosted on other servers:

Lobulated, solid and tan colored (fig. 3A)

Microscopic (histologic) description
  • Lobular with fibrous bands separating solid islands of squamoid cells with variable lymphocytes (mixed mature T and B cells vs immature B cells in thymoma)
  • Tumor cells either have ill defined cell border with vesicular nuclei and prominent nucleoli, or show squamous differentiation with distinct cell borders
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Dr. Shuanzeng Wei and Dr. Zubair W. Baloch, University of Pennsylvania (USA):

Well demarcated tumor nests

Tumor nest

Tumor cells with indistinct cell border

Contributed by Andrey Bychkov, M.D., Ph.D., Kameda Medical Center

Central necrosis

Low power

Fibrous bands

Squamoid cells

Invasive growth


Irregularly shaped lobules in solid pattern

Sharply defined tumor lobule

Plump epithelial cells and small lymphocytes

Images hosted on other servers:

Various images

Cytology description
Cytology images

Images hosted on other servers:

Various images (fig. 2)


to ovoid malignant cells
(fig. 1)

Positive stains
Negative stains
Differential diagnosis
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