1. ¹Angiogenesis Laboratory, Department of Pathology, Research Institute for Growth and Development (GROW), Maastricht University & University Hospital Maastricht, Maastricht NL 6229 HX, The Netherlands
2. ²Translational Cancer Research Group (Lab Pathology University of Antwerp/University Hospital Antwerp, Edegem; Oncology Center, General Hospital St Augustinus, Wilrijk), Antwerp B-2650, Belgium
3. ³Department of Pathology, University Hospitals of Leuven, Leuven B-3000, Belgium
4. ⁴Department of Urology, University Hospitals of Leuven, Leuven B-3000, Belgium

Correspondence: Dr MM Baldewijns, Department of pathology, AZ Maastricht, P. Debeyelaan 25, Maastricht NL 6229 HX, The Netherlands. E-mail: mbald@lpat.azm.nl

Received 12 February 2007; Revised 23 April 2007; Accepted 23 April 2007; Published online 15 May 2007.

Abstract

Clear cell renal cell carcinoma (CC-RCC) is a highly vascularised tumour and is therefore an attractive disease to study angiogenesis and to test novel angiogenesis inhibitors in early clinical development. Endothelial cell proliferation plays a pivotal role in the process of angiogenesis. The aim of this study was to compare angiogenesis parameters in low nuclear grade (n=87) vs high nuclear grade CC-RCC (n=63). A panel of antibodies was used for immunohistochemistry: CD34/Ki-67, carbonic anhydrase IX, hypoxia-inducible factor-1 (HIF-1) and vascular endothelial growth factor (VEGF). Vessel density (MVD – microvessel density), endothelial cell proliferation fraction (ECP%) and tumour cell proliferation fraction (TCP%) were assessed. mRNA expression levels of angiogenesis stimulators and inhibitors were determined by quantitative RT–PCR. High-grade CC-RCC showed a higher ECP% (P=0.049), a higher TCP% (P=0.009), a higher VEGF protein expression (P<0.001), a lower MVD (P< 0.001) and a lower HIF-1 protein expression (P=0.002) than low-grade CC-RCC. Growth factor mRNA expression analyses revealed a higher expression of angiopoietin 2 in low-grade CC-RCC. Microvessel density and ECP% were inversely correlated (Rho=-0.26, P=0.001). Because of the imperfect association of nuclear grade and ECP% or MVD, CC-RCC was also grouped based on low/high MVD and ECP%. This analysis revealed a higher expression of vessel maturation and stabilisation factors (placental growth factor, PDGFB1, angiopoietin 1) in CC-RCC with high MVD, a group of CC-RCC highly enriched in low nuclear grade CC-RCC, with low ECP%. Our results suggest heterogeneity in angiogenic activity and vessel maturation of CC-RCC, to a large extent linked to nuclear grade, and, with probable therapeutic implications.