FGF8 isoform b expression in human prostate cancer

Abstract

Overexpression of fibroblast growth factor 8 (FGF8) mRNA has been previously described in prostate cancer. Of its four isoforms, FGF8b is thought to be the most important in carcinogenesis. We hypothesised that immunodetection of FGF8b in archival prostate cancer specimens is of potential prognostic value. Using a selected cohort of prostate tumours from transurethral (n=30) and radical prostatectomies (n=59), an optimised protocol for FGF8b immunoreactivity was used to corroborate expression with clinical parameters. No expression was observed in benign prostates (n=10). In prostate cancer, immunoreactivity was localised to the malignant epithelium with weak signals in the adjacent stroma. Expression of FGF8b in stage T1 and T2 cancers were 40 and 67%, respectively. In contrast, FGF8b expression was present in 94% of T3 and 100% of T4 cancers. By histological grade, FGF8b was found in 41% of low-grade cancers (Gleason score 4-6), 60% of intermediate-grade cancers (Gleason score 7 and 92% of high-grade cancers (Gleason score 8-10). The intensity of expression was significantly associated with stage (P=0.0004) and grade (P<0.0001) of disease. We further hypothesised that FGF8b overexpression resulted from enhanced transcription and translation rather than from abnormalities involving the FGF8 gene locus. This was tested by means of fluorescent in situ hybridisation in 20 cancer specimens to map the FGF8 gene locus. FGF8 gene copy number in benign and malignant nuclei was found to be similar (2.33+/-0.57 and 2.0+/-0.81, respectively P=0.51). Based on these findings, we propose a multicentre study on cohorts of patients to further evaluate FGF8b as a potential prognostic marker in prostate cancer.

Figures

Figure 1

FGF8b expression pattern in prostate cancer. (A) Benign prostate with no staining for FGF8b. (B) Malignant foci (black arrow) of prostate cancer demonstrating FGF8b positivity in epithelial cells and associated weak stromal signals (yellow arrow). (C) Sections of malignant epithelium adjacent to benign glands (red arrow). (D) FGF8b-negative high-grade prostatic intraepithelial neoplasia from a radical prostatectomy. (E–G) Sections of prostate demonstrating low, moderate and high FGF8b expression, respectively, in different histological grades of cancer.

Figure 2

FGF8 gene locus analysis. Nuclei and chromosomes are stained blue by DAPI as in Materials and Methods. (A, B) Fluorescent in situ hybridisation using a chromosome 10 specific probe (red fluorescent) for analysis of the mean chromosome copy number in benign and malignant prostate sections, respectively. (C) Specific localisation of the green fluorescent-labelled BAC probe to the short arm of chromosome 10 in blood metaphase spreads. (D) Paraffin FISH using fluorescent-labelled BAC probe in a benign prostate section. (E) Paraffin FISH using fluorescent-labelled BAC probe in prostate cancer.