Aim: A low vessel density is a common feature of malignant tumors. We suggested that the expansion of vessel diameter might reconstitute the oxygen and nutritient's supply in this situation. The aim of the present study was to compare the number and diameter of blood vessels in pancreatic and liver carcinoma with normal tissue.
Methods: Tumor induction of pancreatic (DSL6A) or hepatocellular (Morris-hepatoma) carcinoma was performed in male Lewis (pancreatic cancer) and ACI (hepatoma) rats by an orthotopic inoculation of solid tumor fragments (pancreatic cancer) or tumor cells (hepatoma). Six weeks (pancreatic cancer) or 12 d (hepatoma) after tumor implantation, the tumor microvasculature as well as normal pancreatic or liver blood vessels were investigated by intravital microscopy. The number of perfused blood vessels in tumor and healthy tissue was assessed by computer-assisted image analysis.
Results: The vessel density in healthy pancreas (565+/-89 n/mm(2)) was significantly higher compared to pancreatic cancer (116+/-36 n/mm(2)) (P<0.001). Healthy liver showed also a significantly higher vessel density (689+/-36 n/mm(2)) compared to liver carcinoma (286+/-32 n/mm(2)) (P<0.01). The comparison of diameter frequency showed a significant increase of vessel diameter in both malignant tumors compared to normal tissue (P<0.05).
Conclusion: The expansion of endothelial cells during tumor angiogenesis is accompanied to a large extent by an increase of vessel diameter rather than by formation of new blood vessels. This may be a possible adaptive mechanism by which experimental pancreatic and hepatocellular cancers expand their endothelial diffusion surface of endothelium to compensate for inadequate neoangiogenesis.