Immunohistochemical Cal9-9 in primary colonic polyps and polyps synchronous with colorectal cancer.

A prospective study was undertaken to examine the immunohistochemical expression of tumor antigen Cal9-9 in 56 colorectal cancers and 95 colonic adenomas, divided into 65 primary polyps and 30 polyps synchronous with colorectal cancer. Seventy five per cent of tumours were positive for Cal9-9. Antigen was expressed more frequently in advanced Duke's C and D and poorly differentiated colorectal cancer. Overall 51% of adenomas were positive for Cal9-9. Antigen expression correlated significantly with increasing size (p less than 0.001), synchronicity with colorectal cancer (p less than 0.001), severe dysplasia (p less than 0.001) and villous typing (p less than 0.003). Discriminate analysis using the first three variables correctly classified 79% of positive and 89% of negative Cal9-9 results. The similar frequency of antigen expression seen in colorectal cancers and their synchronous adenoma suggests a field change in the tumour bearing colon. Adenomas positive for Cal9-9 may have a greater malignant potential for carcinomatous change.