Regional heterogeneity and complementation in the expression of the tumor-associated glycoprotein 72 epitopes in colorectal cancer.

We analyzed the immunohistochemical expression of three epitopes of the tumor-associated glycoprotein 72 (TAG-72) in whole cross-sections of primary colorectal carcinomas and in regional lymph node metastases using monoclonal antibodies (MAbs) B72.3, CC-49, and CC-83, which recognize distinct carbohydrate antigenic determinants. B72.3, CC-49, and CC-83 reacted with 13 of 27 (48%), 25 of 27 (92%), and 21 of 27 (77%) carcinomas, respectively. The immunoreactivity with lymph node metastases followed a similar pattern; MAb CC-49 was again the most reactive of the three antibodies, since it labeled 13 of 15 metastatic lesions. Positive reactions of the MAbs with the primary tumors were not always predictive of the immunorecognition of their metastases. Distinct areas within whole cross-sections of TAG-72-positive primary carcinomas demonstrated marked differences in the expression of the three epitopes. CC-49 tended to react with the highest number of areas and with the highest percentages of carcinoma cells within each area. In no instances did B72.3 demonstrate reactivity superior to that of either CC-49 or CC-83. Tumors negative for the CC-49 epitope in any area also did not express the other two TAG-72 epitopes. However, the comparison of the immunostaining obtained with each MAb in TAG-72-positive primary lesions revealed areas where CC-83 was clearly more reactive than CC-49. Moreover, one lymph node metastasis, negative for CC-49, was recognized by CC-83. Thus, the combined use of MAbs CC-49 and CC-83 resulted in additive immunostaining of primary and metastatic colorectal carcinoma cells. The study provides evidence of intratumoral heterogeneity in the glycosylation pattern of the TAG-72 antigen in colorectal cancer and emphasizes the advantages of cocktails of anti-tumor-associated antigen MAbs in the immunodetection of colorectal tumor cells.