Tuomela et al. BMC Cancer 2010, 10:596 http://www.biomedcentral.com/1471-2407/10/596 Page 10 of 14 Figure 6 Glucose metabolism. A, Intratumoral distribution of [18F]FDG-derived radioactivity in tumour sections (FGF8b n = 6, VEGF n = 6 and mock n = 5). Uptake intensity is not comparable between these images, since they were not corrected for injected dose or cross-calibrated between separate studies. B, Tumour-to-blood (T/B) uptake ratio of [18F]FDG (T/B ratio) in FGF8b (n = 6), VEGF (n = 6) and mock (n = 5) tumours is expressed as mean ± SD. The accumulation of [18F]FDG was significantly lower (p < 0.05) in FGF8b tumours compared with VEGF and mock tumours. Number of cells/cm3 was determined using TrueCount tubes and flow cytometry. On the right, we show relative uptake of [18F]FDG after balancing the uptake against cell number. C, Immunostaining of the glucose transporter GLUT1 showed decreased staining in VEGF tumours compared with mock and FGF8b tumours (FGF8b n = 5, VEGF n = 4 and mock n = 7 tumours) (p < 0.05 VEGF vs. mock, Bar 200 μm). Analysis was carried out in a blinded manner in three representative non-overlapping fields of the tumours, and the data presented as mean ± SD. induce mature and fully functional capillaries without synergistic actions of other growth factors [53]. These findings made us question whether the capillaries in FGF8b tumours are able to function properly. The performance of blood capillaries was studied by means of the perfusion marker Hoechst 33342, which revealed relatively low perfusion in mock tumours. Func- tional capillaries were seen only in the periphery of the tumours and they were sparse in central parts (Figure 4A). Despite the rich capillary network in FGF8b tumours, very low perfusion was detected, indicating that the rapid growth in comparison with mock tumours was caused by factors other than increased blood flow. It seems that the number of functional capillaries in FGF8b tumours is modest. The vessel-like structures could be a consequence of angiogenic mimicry, and these structures are not able to maintain proper oxygenation and support intratumoral cells. On the other hand, the VEGF tumours seemed to have an adequate number of functional capillaries. VEGF tumours were properly perfused, not only peripherally but also in central areas. Accordingly, the area of necrotic tis- sue in VEGF tumours was negligible. Because of abnormal vasculature, hypoxia is very com- mon in solid tumours. Since morphological evaluation and perfusion studies of the FGF8b tumours indicated that these vessels were not functioning normally, we decided to evaluate the proportion of hypoxic cells in the tumours. We found a significantly reduced T/B uptake