Metastatic bronchioloalveolar carcinoma presenting as a solitary thyroid nodule: Report of a case with fine‐needle aspiration cytopathology

Abstract

Although cancers metastatic to the thyroid are frequently mentioned in autopsy studies, such a finding is quite rare in routine clinical practice. Metastatic non‐small‐cell carcinomas to the thyroid may present a diagnostic dilemma, particularly when they share morphological similarities with primary thyroid tumors. Herein, we report a case of metastatic bronchioloalveolar carcinoma that presented as an isolated left thyroid nodule in a 68‐year‐old woman. The aspirates were cellular and showed numerous papillary‐like tissue fragments, elongated nuclei with prominent nuclear grooves, frequent mitoses, and psammoma bodies. The latter features raised the possibility of papillary thyroid carcinoma. However, also seen were three‐dimensional tumor nests and acinar‐forming fragments. Immunostains (positive for cytokeratin‐7 and carcinoembryonic antigen and negative for cytokeratin‐20 and thyroglobulin) confirmed the metastatic nature of the carcinoma. In a patient with known primary neoplasm, the differential diagnosis of a thyroid nodule should always include a metastatic lesion along with primary neoplasia. Diagn. Cytopathol. 2004;31:43–47.