Expression of endothelial factors in prostate cancer: a possible role of caveolin-1 for tumour progression

Solid tumours need to induce their own vascular supply, and microvessel density (MVD) has emerged as a prognostic factor in several tumours. We hypothesized that mRNA levels of some endothelial factors in prostate cancer tissue would correlate with histologically measured MVD, or other pathological parameters. Expression levels of the endothelial factors CD31, CD34, CD105, CD144, CD146, CAV1 and VEGFR2 were assessed by RT-qPCR in matched freshly frozen normal and tumour tissues from 69 patients that underwent radical prostatectomy. The results were compared to pathological parameters and the MVD in the corresponding paraffin-embedded material, as determined by immunohistochemistry against CD31 and CD34. Comparing mRNA expression in matched normal and tumour samples, only CAV1 showed relevant differences, being down-regulated in tumour tissues (fold change = -1.89, P<0.0001). CAV1 down-regulation correlated with pT category (P=0.006) and the Gleason score (P=0.041). In a univariate analysis, lower CAV1 mRNA expression was associated with biochemical recurrence (P=0.019). By immunohistochemistry, CAV1 was mainly localized in endothelial and stromal cells and showed a weaker staining pattern in the tumour compared to normal tissue. Furthermore, MVD significantly correlated with tumour grade and pT category. There was no significant association between endothelial mRNA expression and histologically determined MVD in tumour tissues, but only a trend for CD31 mRNA (P=0.074) and an inverse trend for CAV1 mRNA (P=0.056). In conclusion, there is only a weak correlation between the mRNA expression of endothelial factors and MVD in prostatic tumour tissue. However, loss of CAV1 mRNA expression may play a role in prostate cancer progression.