DRD2 and prolactin-producing pituitary gland adenoma: The LFS-associated recurrent prolactinoma was predictably resistant to the usual management by dopamine agonists not only due to its large size, elevated Ki-67 proliferation index and clinical relapse, but also to lack of expression of dopaminergic receptors, including D2, encoded by the DRD2 gene (Fig. 6A).