Thus, if one of the factors that has been implicated in the genesis of prolactinomas is the estradiol, because the tumor develops following chronic treatment with the steroid, and the pituitary produces estradiol by acting of aromatase, it is not unreasonable to consider the possibility that the development of pituitary tumors, and in particular the development of prolactinomas, could be related to the local production of estradiol from testosterone through the action of aromatase (see Figure 1). The gene discussed is CYP19A1; the disease is pituitary tumor.