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Radioimmunodetection of Cancer with Radioactive Antibodies to Carcinoembryonic Antigen¹

Division of Experimental Pathology, Department of Pathology [D. M. G., S. B., F. J. P.], and Division of Nuclear Medicine, Department of Radiation Medicine [E. E. K., F. H. D.], University of Kentucky College of Medicine, Veterans Administration Medical Center, and the the Ephraim McDowell Community Cancer Network, Inc., Lexington, Kentucky 40536

Our recent clinical experience in the radioimmunodetection of cancer in 142 patients with a proven history of cancer is summarized. ¹³¹I-labeled affinity-purified goat immunoglobulin G having 70% immunoreactivity with carcinoembryonic antigen (CEA), representing a radiation dose ranging from 0.7 to 2.1 mCi/70 kg patient (2 to 3 µg/kg immunoglobulin G protein), was administered i.v. Anterior, posterior, and lateral radioscans of the chest and abdomen were made routinely at 24 and 48 hr with a -scintillation camera. Computer-assisted processing of the images in order to subtract ^99mTc background radioactivity was used to enhance the tumor-related activity, this method resulting in an average 2.5-fold enhancement of the tumor images. A very high percentage of tumor detection was achieved in most of the epithelial cancers studied. The overall sensitivity (true-positive rate) in the four major cancer types studied was as follows: colorectal cancer, 85%; ovarian cancer, 88%; cervical cancer, 90%; and lung cancer, 71%. The specificity (true-negative rate) of the method was likewise very high, ranging from 83 to 100%. In some cases, tumor radioimmunodetection was positive when other detection methods failed. The smallest tumors detectable by this method of radioimmunodetection appeared to be about 2 cm. Metastatic tumors could be localized in a number of patients with normal plasma CEA titers, although in colorectal, cervical, and lung cancer patients there appeared to be a correlation between positive radioimmunodetection and plasma CEA elevation. In general, however, radioimmunodetection was more reliable in detecting cancer among the patient population studied than were the plasma CEA assay results. High amounts of circulating CEA did not appear to prevent successful cancer radioimmunodetection. No untoward or hypersensitivity reactions were found among the patients studied, even when radioimmunodetection was repeated.

Evaluation of the clinical findings in the 142 cancer patients studied revealed 116 nonneoplastic benign disease conditions, of which only 2 showed some evidence of radioantibody localization (less than 2%). Administration of radiolabeled normal goat immunoglobulin G to 22 cancer patients, some of whom were already shown to be positive for radioimmunodetection with radioactive CEA antibody, resulted in only 4 of 32 tumor sites with some evidence of transient radiolocalization; 3 of these 4 sites were massive lesions at least 10 cm in diameter.

¹ Presented at the UICC Workshop on Radioimmunodetection of Cancer, July 19 to 21, 1979, Lexington, Ky. These studies were supported in part by NIH Grants CA-17742 and CA-25584, by NIH Contract NCI-N01-CB-64011-35, and by the Veterans Administration.

² To whom requests for reprints should be addressed, at the Division of Experimental Pathology, University of Kentucky College of Medicine, MS-409, Lexington, Ky. 40536.