Overexpression of fibroblast growth factors (FGFs) has been implicated in prostate carcinogenesis. FGFs function via their high-affinity interactions with receptor tyrosine kinases, FGFR1 -4. Expression of FGFR1 and FGFR2 in prostate cancer (CaP) was not found to be associated with clinical parameters. In this report, we further investigated for abnormal FGFR expression in prostate cancer and explore their significance as a potential target for therapy. The expression levels of FGFR3 and FGFR4 in CaP were examined and corroborated to clinical parameters. FGFR3 immunoreactivity in benign prostatic hyperplasia (BPH) and CaP (n ¼ 26 and 57, respectively) had similar intensity and pattern. Overall, FGFR4 expression was significantly upregulated in CaP when compared to BPH. A significant positive correlation between FGFR4 expression and Gleason score was noted: Gleason score 7 -10 tumours compared to BPH (Po0.0001, Fisher's exact test), Gleason score 4 -6 tumours compared to BPH (Po0.0004), and Gleason 7 -10 compared to Gleason 4 -6 tumours (Po0.005). FGFR4 overexpression was associated with an unfavourable outcome with decreased disease-specific survival (Po0.04, log rank test). FGF-induced signalling is targeted using soluble FGF receptor (sFGFR), potent inhibitor of FGFR function. We have previously shown that sFGFR expression via a replication-deficient adenoviral vector (AdlllcRl) suppresses in vitro FGF-induced signalling and function in human CaP DU145 cells. We tested the significance of inhibiting FGF function along with conventional therapeutic modalities in CaP, and confirmed synergistic effects on in vitro cell growth (proliferation and colony formation) by combining sFGFR expression and treatment with either Paclitaxel (Taxol s ) or g-irradiation. In summary, our data support the model of FGF system as valid target for therapy in CaP. Prostate cancer is the commonest cancer in men and the second commonest cause of cancer-related death in men, and its incidence is increasing (Woolf, 1995;Boyle et al, 1996). Prostate cancer is an enigmatic disease. It is histologically present in 80% of men over the age of 80 years, but will only clinically manifest itself in about 10%. Increasing use of serum measurement of prostate-specific antigen is facilitating early diagnosis of prostate cancer. There are currently limited prognostic markers that may allow patients found to have early prostate cancer to be stratified into different management plans. Hence, new methods of predicting disease progression are urgently needed.Abnormal expression of peptide growth factors and their highaffinity receptor tyrosine kinases are important in the development and progression of prostate cancer. These mitogens enhance tumour proliferation and invasion while inhibiting apoptosis. Several peptide growth factors have been implicated in prostate cancer development and progression, including insulin-like growth factors, epidermal growth factor and members of the fibroblast growth factors (Byrne et al, 1996;Tennant et al, 1996;Dorkin et...