Radioimmunodetection of carcinoma of the stomach and colorectum by monoclonal antibodies

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Radioimmunodetection using monoclonal antibody to tumor-associated antigen has the potential for the differential deagnosis between malignant and benign tissues. We produced the monoclonal antibodies, GC302 to gastric cancer, and CEA102 to colorectal cancer in our laboratory. The antigen recognized by GC302 is 40K and characterized as an oncofetal antigen in stomach,and also as a differentiation antigen whose localization discriminates between the gastrointestinal tracts of the forgut origin and midgut origin. CEA102 reacted with normal epitherium of fetal colon and almost all cancer of the colorectum. Other cancers or normal tissues such as melanoma, leukemic cells, and fibrous tissues were negative. Therefore GC302and CEA102 are good tool to detect metatatic sites of gastric and colorectal cancer, respectively.After radioimmunoscintigraphy using xenografts could be done successfully, we applied this method to detect metastatic sites of patients with colorectal cancer. Six patients were studied with ^<131>I labeled CEA102, and two showed significant accunulation of antibody by scintigraphy. Moreover, we investigate to compare the excretion of antibody, and its accumulation to tumor between F(ab')_2 and whole CEA102. The results showed F(ab')_2 is better in excretion and accumulation of antibody. Therefore F(ab')_2 allows us to use^<123>I and Emission CT.