['Estrogen receptor beta (ERβ) has been demonstrated to be expressed in prostate carcinoma cells and estrogen signals through ERβ to act as a tumor suppressor in prostate cancer patients. ERβ is thought to regulate the cell cycle of prostate carcinoma cells by controlling the expression of cell cycle regulators including cyclin D1 (CCND1). This interaction is of particular interest as CCND1 has been implicated in the development of prostate cancer.', 'We evaluated ERβ and CCND1 immunoreactivity in human prostate cancer (n\u2009=\u2009112, surgical specimens), and correlated the findings with clinicopathological features of the patients. Subsequent in vitro experiments using PC-3 prostate carcinoma cells were also performed to examine whether estradiol (E2) could change the expression level of CCND1 mRNA.', 'CCND1 immunoreactivity was detected in 78/112 cases (70%), and was significantly correlated with incidence of perineural invasion and ERβ immunoreactivity (P\u2009<\u20090.05). Forty-eight hours incubation with E2 (10\u2009nM) increased the expression level of CCND1 mRNA as well as c-jun (JUN) and c-fos (FOS) in PC-3 cells, and PHTPP (ERβ antagonist) suppressed E2 -induced expression of those mRNAs.'] Is cyclin D1 ( CCND1 ) expression involved in estrogen receptor beta ( ERβ ) in human prostate cancer?