RESUMO
Metastases to the thyroid gland diagnosed by means of fine needle cytology or by excision have been reported in the literature. To our knowledge, metastatic neoplasms to the parathyroid gland have never been described up to now. In this article, we introduce a rare case of metastatic breast carcinoma to a parathyroid adenoma in a 56-year-old woman, which clinically simulated a left thyroid nodule. The patient had a history of left breast carcinoma; the recent discovery of a palpable mass in the left thyroid area had elicited fine needle cytology sampling for its diagnostic evaluation. The obtained cytopathological sample was cellular but limited to a single Diff-Quik-stained smear; hence, no ancillary studies could be entertained. A cytopathological diagnosis of positive for malignant cells of query metastatic breast origin was performed. The permanent histopathological examination of the surgical sample disclosed multiple small foci of metastatic high-grade carcinoma of ductal type within a somewhat atypical adenoma of the parathyroid gland. The cytopathological findings and some differential diagnostic considerations are briefly commented, as well as the deranging imaging data concerning this interesting case.