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11 February 2015 - Case #342

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Thanks to Dr. Cristina Aguilar, The Guthrie Clinic, Pennsylvania (USA), for contributing this case.


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Case #342

Clinical history:
A 54 year old woman had 2 firm thyroid nodules, which were excised.

Microscopic images:

Frozen section slides

Permanent sections

What is your diagnosis?

Click here for diagnosis and discussion:

Diagnosis: Leiomyosarcoma (metastatic)

Tumor cells were immunoreactive (images not provided) for actin, desmin, caldesmon and vimentin, weakly positive for CD68 and had a proliferation rate of 28% with Ki67. They were negative for pan-keratin, TTF1, CD117/c-kit, S100, PAX8, CD34 and Factor VIII.

The tumor is composed of hypercellular fascicles of spindle cells resembling smooth muscle cells, with moderate to occasionally severe pleomorphism. Although mitotic figures are not numerous in the images, Ki67 shows a high proliferation rate of 28%. These histologic features, together with immunoreactivity for smooth muscle markers (actin, desmin, caldesmon) and the high Ki67 is characteristic of leiomyosarcoma. In this case, the patient was reported to have a uterine leiomyosarcoma removed 2 years prior.

Although the thyroid gland is very vascular, clinical metastases to this gland are uncommon, accounting for only 1 - 3% of thyroid malignancies, usually from kidney, lung, breast, esophagus or uterus (Head Neck Pathol 2009;3:217, Cancer 1997;79:574). In patients dying of cancer, 10 - 24% have metastases at autopsy in the thyroid gland. The differential diagnosis also includes direct extension of tumors from the pharynx, larynx, trachea, esophagus and neck, which are usually squamous cell carcinomas.

Metastatic leiomyosarcoma to the thyroid gland is very rare (Thyroid 2007;17:1295, Obstet Gynecol 2002;100:1122). The differential diagnosis includes the more common anaplastic carcinoma (Cancer 1988;62:2558). Excision of isolated metastases may be effective treatment.

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