Metastases to the Thyroid: Potential Cytologic Mimics of Primary Thyroid Neoplasms

Abstract

Secondary tumors of the thyroid gland, although uncommon, can sometimes pose as diagnostic dilemmas on fine-needle aspiration cytology, frequently mimicking primary thyroid neoplasms. An accurate diagnosis of such lesions, however, is critical for patient management and prognosis. The present study reviews the cytologic aspects of secondary involvement of the thyroid, listing the most common primary malignancies that metastasize to this gland. Knowledge of such morphologic aspects, combined with prompt clinical correlation, is essential for the cytopathologist to achieve a proper, definite diagnosis.

A Rare Case of Uterine Leiomyosarcoma with Metastasis to the Thyroid Gland

“…A detailed IHC panel should include SMA, desmin, cytokeratin pool AE1/AE3, and S-100 as a melanocyte marker combined with thyroid markers, in order to help distinguish a sarcoma from other spindle cell malignancies [2]. From the clinical point of view, some clues should be factored into the equation, for example, the presence or absence of the regional lymph node involvement.…”

“…Epidemiologic studies state that of all the thyroid malignancies, approximately 2% to 3% are secondary to metastasis [3]. As reported by Pastorello and Saieg, adenocarcinomas predominantly from the kidney, breast, and lungs and squamous cells carcinomas mostly from the head and neck account for the most common metastatic cancers to the thyroid [2].…”

“…It is well documented that thyroid metastases may mimic primary thyroid malignancies. Primary and secondary thyroid leiomyosarcoma can resemble anaplastic thyroid carcinoma (ATC), as well as medullary thyroid cancer (MTC) and melanoma, since they all can present as spindle cell tumors on cytology [2,8]. We present this case of a metastatic uterine leiomyosarcoma to the thyroid to review the differential diagnosis of spindle cell neoplasms.…”

Rhabdoid cells in the fine needle aspirate of a neck mass in a patient with history of melanoma: Anaplastic thyroid carcinoma

“…Clinically, it presents in older patients (median age 70 years) as a rapidly expanding large (median 6.4 cm) neck mass, accompanied by symptoms of invasion of neighboring structures, such as hoarseness, dysphagia, and dyspnea. Although melanoma aspirates tend to more cellular than aspirates from ATC, both tumors have extreme morphologic variability and show extensive morphologic overlap making their differentiation difficult if not impossible on morphologic grounds alone 21,22. 4-6 Binucleated and multinucleated tumor cells and foreign-body osteoclastic giant cells can also be present.…”

“…Although melanoma aspirates tend to more cellular than aspirates from ATC, both tumors have extreme morphologic variability and show extensive morphologic overlap making their differentiation difficult if not impossible on morphologic grounds alone. 21,22 To compound the difficulties of the differentiation between from ATC, metastatic melanomas have been reported to express a number of epithelial markers, including cytokeratins, carcinoembryonic antigen, and EMA, and may loose some or even all 23 of their characteristic markers (HMB45, Melan-A, tyrosinase, and even S-100 and SOX-10).…”