Differences in angiogenesis and collagenesis between exophytic and flat adenomas of the colorectal mucosa

A connective tissue core is present in exophytic colorectal adenomas but not in flat adenomas. In the present work, the occurrence of collagen (the principal and most abundant component of the connective tissue) and of microvessels was investigated in 68 colorectal adenomas (35 exophytic and 33 flat). Tissue sections were alternatively challenged with Sirius stain (to evidence collagen) and with von Willebrand Factor (to evidence endothel-lined microvessels). The reactions were semiquantitatively estimated and the number of microvessels quantitatively assessed. Both collagen and microvessels were moderately to markedly increased in 34 of the 35 exophytic adenomas, but only slightly increased or normal in all 33 flat adenomas. Since factors released from neoplastic cells evoke microangiogenesis and those released from mesodermal cells evoke collagenesis, it would appear that the molecular information aimed at generating both microvessels and collagen in the connective tissue core of exophytic adenomas emanates from two different cell systems. The reason(s) for the inability of neoplastic cells and mesodermal cells to induce microangiogenesis and collagenesis in flat adenomas remains unclear.