CD31 and collagen IV immunostaining. Mean blood vessel wall thickness visualized through A CD31 (endothelial cells) and B collagen IV (basement membrane). Both are abnormally thick as compared to healthy liver control tissue, which is denoted by the dashed line. C shows that mean blood vessel density assayed using CD31 staining is greatest in 3 week old MFP tumours. D indicates mean vascular area as a measure of blood vessel size and capacity. Their small size categorizes them as microvasculature. All data are shown as the mean of n = 4 animals ± SD. Starred lines connecting bars denote statistical significance, P < 0.05.