Malignant transformation in human colorectal mucosa as monitored by distribution of laminin, a basement membrane glycoprotein.

The distribution of laminin, a basement membrane glycoprotein, was studied by indirect immunofluorescence technique using rabbit anti-laminin serum in fifty-seven samples of normal, hyperplastic, adenomatous and carcinomatous colorectal tissue. As judged by the expression of laminin normal, hyperplastic and adenomatous colorectal mucosa were characterized by a continuous, linear basement membrane. A thick band-like basement membrane was seen under the surface epithelium and at the mouths of the crypts in normal and hyperplastic mucosa. The adenomatous epithelium was uniformly characterized by a thin, linear basement membrane. In contrast, marked alterations were constantly observed in colorectal carcinomas and their metastases, which showed a discontinuous, linear or patchy basement membrane. Our study suggests that the expression of laminin is related to cellular differentiation, and the thickness of the laminin-positive basement membrane parallels with the epithelial maturation of normal and hyperplastic colorectal mucosa and with the failure of the epithelial differentiation in adenomas. In colorectal carcinomas and their metastases the distribution of laminin is constantly altered and the severity of the alterations correlates with the histological grade of these tumours.