Papillary carcinoma of thyroid metastatic to adenocarcinoma in situ of lung: report of an unusual case.

The tumor-to-tumor metastasis is a rare event. The lung tumors are the most common donor tumors in tumor-to-tumor metastasis, but are exceedingly rare as a recipient. Here, we report a case of papillary thyroid carcinoma (PTC) metastasizing to adenocarcinoma in situ (AIS, formerly bronchioloalveolar carcinoma) of the lung in a 44-year-old woman who underwent total thyroidectomy for PTC 8 years ago. To the best of our knowledge, the present case is the first case reporting on PTC metastasized to AIS. A review of the relevant literature is presented.