Pulmonary metastasis of a papillary thyroid carcinoma and primary lung adenocarcinoma: two coincident carcinomas at the same location.

Tumor-to-tumor metastasis is a fairly rare phenomenon. The lung cancers are the most common donors, but are exceedingly rare as recipients. Here we report a case of a lung adenocarcinoma acting as the recipient of papillary thyroid carcinoma, with multiple spreading foci of the two cancers in the lung simultaneously. The morphology and immunohistochemistry (Napsin-A, Thyroglobulin) are very important in differential diagnosis of lung primary adenocarcinoma and metastatic papillary thyroid carcinoma. The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2069496615891134.