Two rare thyroid tumours with strange names:

Dr Sampurna Roy MD


Did your pathologist use words like CASTLE  to define your disease ?  She is definitely not talking about an exotic medieval architecture.

When a pathologist uses words like "CASTLE" or 'SETTLE"  it has an entirely different meaning.

Here is a brief summary of these two exceedingly rare tumours.


CASTLE (Carcinoma showing thymus-like differentiation ) is a rare malignant  tumour.

It invades the lower portion of the thyroid gland and sometimes the extrathyroidal soft tissue of the neck.

The lesion was first described as an intrathyroid epithelial thymoma by Miyauchi et al in 1985 and was later designated CASTLE by Chan and Rosai.

It usually affects middle aged and elderly patients.

The histopathology of CASTLE is characterized by a pushing, expansive growth pattern, lobulated appearance, tumour nests divided by thick fibrous band, presence of lymphocytes  and occasional mitosis, absence or limited necrosis.

Immunoreactivity for CD5 is almost always constant.


CASTLE tumour of the neck: a rare location of a malignant tumour of the thymus

Extrathyroid carcinoma showing thymus-like  differentiation (CASTLE): a new case report and review of the therapeutic role of neck dissection and radiotherapy.


SETTLE (Spindle epithelial tumour with thymus-like differentiation) is a tumour of low malignant potential with distant metastases developing some years after diagnosis.

This tumour occurs predominantly in young patients.

The patients present with a painless thyroid mass.

This highly cellular tumour is composed of interlacing to reticulated fascicles of spindle cells that are positive for pan-cytokeratin 

The fascicles of spindle cells merge into epithelial structures which can be in the form of cords, tubules or papillae.

In some cases glandular structures are lined by mucinous or respiratory epithelium.

Histologically, the tumour shows similarity to synovial sarcoma. However, synovial sarcoma, is a more mitotically active, aggressive tumour displaying only patchy immunopositivity with epithelial markers.

It is important to differentiate this indolent tumour from the aggressive anaplastic carcinoma of thyroid.



Spindle epithelialtumour with thymus-like element (SETTLE): the predominantly monophasic variant.

Spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid with prominent mitotic activity and focal necrosis.

Now you know all about two rare thyroid tumours with strange names.

It is time for you to SETTLE down in a comfortable chair and dream about building a CASTLE in the air.

Share on Social Media