Tuomela et al. BMC Cancer 2010, 10:596 http://www.biomedcentral.com/1471-2407/10/596 Page 9 of 14 Figure 5 Relationship between tumour hypoxia and proliferation. Localisation of areas positively stained for HIF1a and Ki67 was visually detected from microscope images in FGF8b and mock tumours. The arrows show positive HIF1a staining and negative Ki67 staining in A and B, and C and D. C and D are captions from the indicated areas in A and B, respectively (Bar 200 μm). The purpose of this study was to evaluate the role of angiogenesis and tumour oxygenation in stimulation of growth of PC-3 prostate xenografts representing com- monly hypoxic prostate cancer. Morphologic evaluation of PC-3 tumours overexpressing FGF8b, as well as those over-expressing VEGF, showed angiogenic morphology overall, compared with mock tumours. According to the results of our previous studies, FGF8b may be a key regu- lator of prostate cancer angiogenesis, supporting tumour growth [20]. We have previously shown that FGF8b increases angiogenic capacity in breast cancer cells and increases vessel sprouting in a chorion allantoic membrane assay [34,35]. In the present study, immunostaining with the endothelial marker CD31 confirmed that both FGF8b- and VEGF-expressing tumours had rich networks of capil- laries, while in mock tumours the capillary network was sparse and individual capillaries were smaller. However, the capillary networks in angiogenic FGF8b- and VEGF- expressing tumours were not similar. Both tumour models showed large numbers of capillaries, but the capillary net- work was more distorted and non-continuous in FGF8b tumours. Areas of cisternal spaces filled with blood were also detected in FGF8b tumours. The accelerated growth rate of both FGF8b and VEGF tumours indicated an increased vessel capacity to support and contribute to tumour growth. FGF8 has also been shown to stimulate the rate of proliferation of PC-3 cells in vitro [20,36], while VEGF is a mitogenic factor affecting endothelial cells only. In the present study, the number of Ki67-positive cancer cells was significantly increased in both FGF8b and VEGF tumours (Figure 3). However, morphological examination of the tumours revealed significantly widened areas of necrosis in FGF8b tumours compared with the others. It has been previously shown that FGFs may not be able to