RP215 monoclonal antibody was shown to recognize specifically a carbohydrate-associated epitope of cancer cellderived immunoglobulins designated as CA215.Previous studies suggest that CA215 is expressed by all human cancer cell lines and tissues in both membrane-bound and secreted forms and may be an ideal target for therapeutic treatments of human cancer with humanized RP215-related antibodies.Based on the results of large scale immunohistochemical studies (50-110 cases each), the following types of cancers revealed high percentages of positive staining with RP215: Esophagus (75%), Stomach (50%), Colon (50%),Ovary (60%), Breast (35%), Lung (35%), Cervix (80%) and Endometrium (80%).Nude mice experiments were performed to see if RP215 has any inhibitory effect on the growth of cancers in vivo.Following injection of a single dose (10 mg/Kg) of I-13 l-labeled, RP215 (Specific activity, 12.5 iCi/mg), the tumor size (OC-3-VGH ovariancancer cells) was reduced to 30% of the untreated control in two weeks.By injecting the same dose, the unlabeled RP215 also reduced the tumor size to 50% during the same period.The antibody was found to have little effect on the body weight of these animals.No apparent toxicity was observed upon antibody treatment (I-13 1-labeled or unlabeled).The results of these studies clearly established proof of concepti± and set the next stages of clinical trial studies in humans with humanized RP215.