Tumor-to-tumor metastasis to follicular variant of papillary carcinoma of thyroid.
OBJECTIVE
To describe and document tumor-to-tumor metastases in the thyroid gland.


RESULTS
In this series we describe 3 cases of tumor-to-tumor metastasis in which the recipient tumor was a follicular variant of papillary thyroid carcinoma. The donor tumors and sites were small cell carcinoma of the lung, neuroendocrine carcinoma probably of pancreatic origin with initial presentation as liver metastasis, and clear cell carcinoma of the kidney with metastasis to liver and pancreas. The donor tumor cells infiltrated the substance of the follicular variant of papillary thyroid carcinoma, the nontumorous thyroid parenchyma, and the lymphovascular spaces. Small cell carcinoma and neuroendocrine carcinoma showed positive reactivity for neuroendocrine markers and were negative for thyroglobulin and calcitonin. The follicular variant of papillary thyroid carcinoma showed positivity with thyroglobulin and cytokeratin 19.


CONCLUSIONS
Although tumor-to-tumor metastases in thyroid gland are exceedingly rare, one should be aware of this phenomenon as the metastatic lesion may simulate a thyroid primary. History of a previous tumor and immunohistochemical stains can be helpful in distinguishing between primary and metastatic thyroid neoplasms.
Baloch
Z W
ZW
Department of Pathology, University of Pennsylvania Medical Center, Philadelphia 19104, USA.
LiVolsi
V A
VA
D018262:Adenocarcinoma, Clear Cell / Q000473:pathology / Q000556:secondary; D000368:Aged; D001706:Biopsy; D002291:Carcinoma, Papillary / Q000473:pathology*; D018288:Carcinoma, Small Cell / Q000473:pathology / Q000556:secondary; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000473:pathology; D008113:Liver Neoplasms / Q000473:pathology / Q000556:secondary; D008175:Lung Neoplasms / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009378:Neoplasms, Multiple Primary / Q000473:pathology*; D010190:Pancreatic Neoplasms / Q000473:pathology; D013964:Thyroid Neoplasms / Q000473:pathology / Q000556:secondary*