Tumor-to-tumor metastasis of the central nervous system.

Tumor-to-tumor metastasis is a well recognized phenomenon. Although any tumor may be potential recipient of metastasis, renal cell carcinoma and meningioma are the most common malignant and benign recipients, respectively, whereas the lung and breast are the most common metastatic donors respectively, in both settings. Patients with hereditary cancer syndromes may be at higher risk for the development of tumor-to-tumor metastases. The most common pattern of tumor-to-tumor metastasis for intracranial neoplasms is the type in which an aggressive high-grade malignancy serves as the source of tumor and a more indolent neoplasm serves as the recipient tumor. The development of tumor metastasis from a second primary malignancy is uncommon and remains biologically puzzling. Its low incidence has made its full biological characterization evasive. Although rare, neurosurgeons should be aware of the entity of tumor-to-tumor metastasis.