AIM:A low vessel density is a common feature of malignanttumors.We suggested that the expansion of vessel diametermight reconstitute the oxygen and nutritient’s supply inthis situation.The aim of the present study was to comparethe number and diameter of blood vessels in pancreatic andliver carcinoma with normal tissue.METHODS:Tumor induction of pancreatic(DSL6A)orhepatocellular(Morris-hepatoma)carcinoma was performedin male Lewis(pancreatic cancer)and ACI(hepatoma)ratsby an orthotopic inoculation of solid tumor fragments(pancreaticcancer)or tumor cells(hepatoma).Six weeks(pancreaticcancer)or 12 d(hepatoma)after tumor implantation,thetumor microvasculature as well as normal pancreatic or liverblood vessels were investigated by intravital microscopy.Thenumber of perfused blood vessels in tumor and healthy tissuewas assessed by computer-assisted image analysis.RESULTS:The vessel density in healthy pancreas(565±89n/mm~2)was significantly higher compared to pancreaticcancer(116±36 n/mm~2)(P<0.001).Healthy liver showed alsoa significantly higher vessel density(689±36n/mm~2)comparedto liver carcinoma(286+32n/mm~2)(P<0.01).The comparisonof diameter frequency showed a significant increase ofvessel diameter in both malignant tumors compared tonormal tissue(P<0.05).CONCLUSION:The expansion of endothelial cells duringtumor angiogenesis is accompanied to a large extent by anincrease of vessel diameter rather than by formation of newblood vessels.This may be a possible adaptive mechanism bywhich experimental pancreatic and hepatocellular cancersexpand their endothelial diffusion surface of endothelium tocompensate for inadequate neoangiogenesis.Ryschich E,Schmidt E,Maksan SM,Klar E,Schmidt J.Expansion ofendothelial surface by an increase of vessel diameter during tumorangiogenesis in experimental hepatocellular and pancreaticcancer.World J Gastroenterol 2004;10(21):3171-3174http://www.wjgnet.com/1007-9327/10/3171.asp AIM: A low vessel density is a common feature of malignant tumors. We suggested that the expansion of vessel diametermight 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 andliver carcinoma with normal tissue. METHODS: Tumor induction of pancreatic (DSL6A) orhepatocellular (Morris-hepatoma) carcinoma was performed in male Lewis (pancreatic cancer) and ACI (hepatoma) rats ACH (hepatoma) rats in an orthotopic inoculation of solid tumor fragments (pancreatic cancer) or tumor cells (hepatoma). Six weeks (pancreatic cancer) or 12 days (hepatoma) after tumor implantation, the tumor microvasculature as well as normal pancreatic or liverblood vessels were investigated by intravital microscopy. 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 ± 89n / mm ~ 2) was significantly higher than pancreatic cancer (116 ± 36n / mm ~ 2 (P <0.001) .Healthy liver showed also significantly higher vessel density (689 ± 36 n / mm 2) compared to liver carcinoma (286 + 32 n / mm 2) ofvessel diameter in both malignant tumors compared to tonormal 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 cells. This may be a possible adaptive mechanism bywhich experimental pancreatic and hepatocellular cancersexpand their endothelial diffusion surface of endothelium tocompensate for inadequate neoangiogenesis. Ryschich E, Schmidt E, Maksan SM, Klar E, Schmidt J. Expansion of endothelial tumors by an increase of vessel diameter during tumorangiogenesis in experimental hepatocellular and pancreatic cancer. World J Gastroenterol 2004; 10 (21): 3171-3174http: //www.wjgnet.com/1007-9327/10/3171.asp