Although up to 24% of metastatic cancers have been reported to involve the thyroid gland, they are clinically rarely encountered. The incidence of metastasis to the thyroid gland in autopsy series varies from 1.25% to 24%. Patients usually have widespread metastasis when there is metastasis to the thyroid gland; because of that, metastasis to the thyroid gland is usually considered as a terminal event. When a patient has a history of a primary carcinoma elsewhere other than the thyroid, even when the primary tumor has been completely excised, a mass in the thyroid gland following that primary tumor should be treated as a metastatic lesion until proved otherwise. Primary tumor origin is usually kidney, lung, breast, esophagus or uterus.
Available from the files of the Department of Pathology at the Uludag University Hospital, four secondary thyroid tumors are included in this study. The primary tumor is known in all but one cases, and these are Renal Cell Carcinoma (RCC), esophageal Squamous Cell Carcinoma (SCC), and adenocarcinoma involving distal esophagus and cardia. In the case with the unknown primary, the histology revealed SCC. SCC with the unknown primary and the metastatic adenocarcinoma were diagnosed with Fine Needle Aspiration Biopsy (FNAB). Metastatic RCC and esophageal SCC were diagnosed with biopsy. The time to detection of thyroid metastasis after primary tumor diagnosis was 9 years in RCC and 4 months in esophageal SCC. The adenocarcinoma case presented with widespread metastasis before the primary tumor was identified. The other SCC case could not be followed up, so the primary tumor could not be detected.
As secondary tumors are rarely encountered, we present 4 cases of metastatic tumor to the thyroid with their histopathological properties.
Keywords: Metastatic tumors, thyroid gland