NR4A1 and meningioma: Meningioma has been reported as the most common recipient tumor in cases of tumor-to-tumor metastasis [3], and several biological factors are thought to contribute to this susceptibility, including rich vascularization, low metabolic activity, immunological tolerance, expression of adhesion molecules such as E-cadherin and mesothelin, high collagen and lipid content, and the presence of hormone receptors (estrogen and progesterone) [11-14].