Immunohistochemical staining of colorectal tissues with monoclonal antibodies to ras oncogene p21 product and carbohydrate determinant antigen 19-9.

Two monoclonal antibodies were applied to benign, dysplastic, and malignant human colorectal tissues using immunohistochemical techniques on formalin fixed paraffin embedded material. RAP-5 antibody is directed against a synthetic peptide, reflecting an amino acid sequence of the ras oncogene p21 protein product. Despite using several different techniques and antibody dilutions differential staining between the various epithelial populations was not obtained. RAP-5 also showed other tissue components such as plasma cells, histiocytes, fibroblasts, smooth muscle and vascular endothelium. CA19-9 antibody recognizes an epithelial surface carbohydrate antigen originally derived from a human colorectal carcinoma cell line: it did not stain normal colorectal mucosa or adenomatous polyps, but showed focal expression of variable strength in regenerative, dysplastic, and cancerous mucosa in ulcerative colitis, and in non-colitic colorectal carcinoma. Neither antibody was found to be a reliable marker of the evolution of malignant mucosal changes, although CA19-9 may be of limited use in confirming adenocarcinoma of gastrointestinal origin.