Distribution of gelatinase B (MMP-9) and type IV collagen in colorectal carcinoma.

Gelatinase B (92 kD, matrix metalloproteinase-9, MMP-9), an enzyme capable of degrading several connective tissue components, was demonstrated by immunolocalization in all specimens of colorectal carcinoma (n = 40), but its distribution between specimens was variable. MMP-9 expression was more frequently observed in advanced tumour stages and was especially prevalent at the side and deep margins of the tumours, and ulceration sites. MMP-9 staining was observed for transformed epithelial cells, macrophages and neutrophils, but seldom for vascular or stromal cells. By contrast, the enzyme was absent from epithelial cells of normal mucosal tissue. Immunostaining of type IV collagen, the major structural component of basement membranes, revealed a general depletion or loss of these structures both within the tumours and at the tumour margins. Dual immunolocalization of MMP-9 and type IV collagen demonstrated that MMP-9 expression at specific sites in the tumour was often inversely related to the distribution of type IV collagen. MMP-9 expression was most pronounced at the invasive tumour margins and in microfoci where tumour cells were in close proximity to inflammatory cells. Such observations support the concept that localized proteolytic and collagenolytic activities contribute to the invasive properties of colorectal tumours.