Papillary thyroid carcinoma metastasizing to anaplastic meningioma: an unusual case of tumor-to-tumor metastasis.

Tumor-to-tumor metastasis is a relatively uncommon entity, whereby the so-called 'recipient' tumor is involved by another biologically unrelated 'donor' tumor. Intracranially, meningioma (WHO grade 1) is the most common recipient tumor, while breast and lung cancers are the most common donor tumors. We present an unusual case of intracranial tumor-to-tumor metastasis involving papillary thyroid carcinoma (PTC) believed to have metastasized to an anaplastic meningioma (WHO grade 3).