Some meningiomas are known to be hormone-sensitive as evidenced by the following possible reasons: (1) meningiomas are three times more common in females than males when they are in their reproductive years; (2) there is an association between meningiomas and breast cancer; (3) the use of exogenous female sex steroids has been shown to increase the risk of meningiomas; and (4) a large majority of meningiomas express progesterone receptors [2]. This evidence concerns the gene PGR and meningioma.