Answer: Metastatic neoplasm

Histology: A thyroid lobectomy was performed revealing a poorly defined nodule within the substance of the thyroid. The cells within the nodule were large, they had abundant cytoplasm and prominent nucleoli.

Discussion: Most nodules in the thyroid arise in the thyroid. Metastases to the thyroid, however, can and do occur. While these metastases most often occur in the setting of widespread disease, some can mimic a primary neoplasm of the thyroid. Cancer can spread to the thyroid either by direct extension (from cancers of the larynx, esophagus, etc.) or by hematogenous spread. The primary cancers that most commonly metastasize to the thyroid include breast, lung, melanoma and kidney. In this case, the patient was known to have a history of melanoma and an immunostains for melan-A were positive.