CARCINOMAS METASTATIC TO FOLLICULAR ADENOMAS OF THE THYROID-GLAND - REPORT OF 2 CASES

Metastases to the thyroid gland are an uncommon occurrence, and metast asis to a preexisting thyroid neoplasm is even more rare. We report tw o cases of tumor-to-tumor metastasis where a prostatic and a breast ca rcinoma metastasized to follicular adenoma of the thyroid gland. The m etastatic process in case 1 was initially diagnosed by fine-needle asp iration biopsy and later confirmed with the hemithyroidectomy. Immunos taining for prostate-specific antigen and prostatic acid phosphatase i n case 1 and estrogen and progesterone receptors in case 2 demonstrate d strong immunoreactivity in the metastatic tumor cells. Flow cytometr ic DNA analysis of the primary and the metastatic tumors in both cases demonstrated stemline fidelity that supported their association. Our cases exemplify why attention should be given to the possibility of me tastasis when distinctly different morphologic features are seen in an otherwise typical tumor and the utility of ancillary tests that may a ssist in establishing the diagnosis.