Fine Needle Aspiration Cytology of a Thyroid Metastasis of Metaplastic Breast Carcinoma: a Case Report

Background: Metaplastic breast carcinoma is defined as mesenchymal and/or squamous cell components associated with ductal carcinoma. Because of the heterogeneous nature of this tumor, cytologic interpretation on fine needle aspirates can be quite challenging. This is especially true of metastatic lesions of this rare tumor type. Metastasis to the thyroid has not been previously reported.

Case: A 57-year-old woman with a history of metaplastic breast carcinoma for which she underwent mastectomy, chemotherapy and radiation therapy 2 years earlier presented with a fast-growing left thyroid mass with progressive hoarseness and dysphasia. Clinical presentation and findings from a neck computed tomographic scan were strongly suggestive of a primary thyroid malignancy. The aspirate specimen was composed of scant, highly atypical epithelial cells in a background of an abundant chondromyxoid matrix and scattered, benign follicular cells. A literature review confirmed the novelty of this case.

Conclusion: This case emphasizes the value of clinical information and the importance of generous sampling in achieving a correct diagnosis of metastatic metaplastic carcinoma.