The relationship between estrogen and pituitary prolactinoma is well documented. The biological effects of estrogen are mainly mediated by estrogen receptor alpha (ER alpha). Several lines of evidence demonstrate that growth factors such as pituitary tumor transforming gene (PTTG), basic fibroblast growth factor (bFGF), transforming growth factor beta 1 (TGF beta 1), transforming growth factor beta 3 (TGF beta 3), and transforming growth factor beta receptor type II (TGF beta RII) play an important role in prolactinoma pathogenesis induced by estrogen, but the relationship between ER alpha and such growth factors is still unclear. The aims of this study are to investigate the functional role of ER alpha in proliferation, prolactin (PRL) secretion, and expression of the above-mentioned growth factors in MMQ cells in the absence of estrogen and to discuss the feasibility of using an estrogen receptor antagonist to treat prolactinoma. Fulvestrant, a "pure" antiestrogen without any estrogen-like activity, was used to block expression of ER alpha in the MMQ cell line. Proliferation and PRL secretion of MMQ cells were measured using CellTiter 96(A (R)) AQueous One Solution Cell Proliferation Assay (MTS) and the enzyme-linked immunosorbent assay (ELISA) method. Levels of ER alpha, PTTG, bFGF, TGF beta 1, TGF beta 3, and TGF beta RII were analyzed by real-time polymerase chain reaction (PCR) and Western blot. Fulvestrant significantly inhibited cell proliferation (up to 60.80%) and PRL secretion (up to 77.95%), and changed expression of TGF beta 3 and TGF beta RII in the absence of estrogen. In conclusion, ER alpha plays an important functional role in proliferation and PRL secretion of pituitary prolactinomas and also can change expression of some growth factors even under the condition of no estrogen. Fulvestrant could potentially be an effective therapy for treating such tumors.