MICROVASCULAR STRUCTURE OF BENIGN AND MALIGNANT-TUMORS OF THE COLON IN HUMANS

Studies of experimental tumors in rodents indicate that there are morp hological abnormalities of the tumor microcirculation compared to norm al tissues. The aim of this study was to examine the structure of the microvasculature in benign and malignant colonic tumors in humans usin g microvascular casting techniques. There were 15 adenocarcinomas, fou r benign sporadic adenomas, and three specimens from patients with fam ilial adenomatous polyposis (FAP). A cast of the microvessels of these tumors was prepared by intraarterial administration of acrylic resin (Mercer) and the cast examined by scanning electron microscopy. Quanti tative measures of the microvasculature were obtained from histologica l sections using stereological techniques in four carcinomas, two spor adic adenomas, and 12 adenomas from patients with FAP. Vascular casts of benign colonic adenomas showed that the microvasculature had a simi lar organization to normal colon, However, capillaries and venules wer e elongated and had increased diameters compared to normal. In adenoma s greater than 3 mm in diameter, there was an increased density of mic rovessels in the spaces between tumor cells. Vascular casts of colonic carcinomas were characterized by a disorganized structure and increas ed density of microvessels. The organization of microvessels within ca rcinomas had a similar overall pattern to normal colon. However, the i ncreased number and density of microvessels resulted in formation of n odular dusters of capillaries, formation of ''sheets'' of frequently a nastomosing capillaries, or almost complete packing of the interstitia l spaces of the tumor by capillaries in places. Most capillaries had a long and tortuous course and numerous capillary sprouts were identifi ed. Tumor microvessels had greater mean diameters than normal, Extrava sation of resin from microvessels in carcinomas was frequently seen. T he vascular volume of carcinomas (23.1% +/- 12.2), sporadic adenomas ( 16.3% +/- 3.4), and adenomas >3 mm diameter in patients with FAP (17.7 % +/- 3.0) were significantly greater than in normal colon (11.0% +/- 4.2). This study indicates that there is an increased vascular density in benign and malignant tumors of the colon compared to normal colon. The presence of profusely anastomotic microvessels and frequent capil lary sprouts is evidence of active neovascularization and suggests con trol of tumor growth could be achieved by modifiers of angiogenesis.