Patterns and composition of basement membranes in colon adenomas and adenocarcinomas

We studied the distribution of type IV collagen and type VII collagen in the basement membranes of normal mucosa of the colon, adenomas, and adenocarcinomas using immunoperoxidase and immunofluorescence techniques. In normal mucosa, we found regular type IV collagen-positive basement membranes, lining vascular structures and mucosal epithelia. These basement membranes, however, lacked type VII collagen. In adenomas of the colon, intact basement membranes were observed through type IV collagen staining. Type VII collagen staining was also detected, but only in connection with dysplastic epithelium. Adjacent to the dysplastic epithelium in adenomas, histologically normal epithelium also showed type VII collagen staining along the basement membrane, but this was restricted to the epithelium of the luminal surface. These areas were also investigated for expression of keratins 8, 18, and 19, and keratins 5 and 8 (monoclonal antibodies NCL-5D3 and RCK 102, respectively), but altered differentiation was not detected using this technique. In adenocarcinomas of the colon, type IV collagen was irregularly deposited in the basement membrane of neoplastic tubules. Type VII collagen staining was detected only in well or moderately differentiated carcinomas and in higher amounts. Our findings therefore reveal a transient expression of type VII collagen in the transition of dysplastic epithelium into carcinoma, suggesting the involvement of type VII collagen in the process of early invasion.