Tumor scanning with intravenous I-131 HSA.

Abstract

Direct radioisotopic scan delineation of malignant neoplasms has been restricted, until recently, to certain intracranial tumors, some bone metastases, and tumors of unique biological properties such as differentiated thyroid adenocarcinomas and chondrosarcomas. Reports by Sodee et al. (5), Bolliger and his co-workers (1), and especially those by Finney and Collier and their associates (3, 4), have suggested the possibility of a much wider application of radioisotope scanning to the detection of deep-seated human malignant tumors. We (2) elected to follow the technics outlined by Collier et al., and in a group of 16 patients scanning was attempted after arterial perfusion of the tumor area with dilute hydrogen peroxide solution followed by a radioactive tracer, usually I131-labeled human serum albumin (I131 HSA). In the course of this experience, we found that I131 HSA localized not only in tumor but in certain norma structures such as the stroma of the uterine fundus, and that hydrogen peroxide appeared to have little to do with selective localization, either in tumor or normal tissue (2). Accordingly, we undertook a series of laboratory experiments in albino rabbits in which bilateral hind leg transplants of V-2 squamous-cell carcinoma had been made. We performed arterial perfusion of each hind leg with I131 HSA and other tracers, both with and without certain adjuvants such as dilute hydrogen peroxide solution and nitrogen mustard. Animals were sacrificed, and samples of tumor and nearby normal host tissue were removed for histological study and radiological assay. Results (TABLE I), obtained as counts/min./ g of tissue, show that tumor/nontumor counting rate ratios of the order of 4∶ 1 were achieved within an hour after arterial perfusion with 100 µc I131 HSA alone. These ratios, which rose steadily to about 12∶ 1 at twenty-four hours, and thereafter fell, did not appear to be significantly influenced by prior perfusion with hydrogen peroxide, nitrogen mustard, or any other agent tested. Counting rates were such that useful tumor scans could be made. Intrigued by this phenomenon, we decided to determine whether or not it was the result of arterial perfusion with its attendant high tracer concentration. In a group of tissue distribution experiments, I131 HSA was injected intravenously into the ear veins of V2-tumor-bearing rabbits. The animals were sacrificed at one or twenty-four hours thereafter, and TABLE I shows that tumor/nontumor ratios were of about the same order of magnitude as those achieved by arterial perfusion with I131 HSA, indicating that tracer deposition was largely independent of the route of administration. Counting rates likewise were not significantly altered, and good tumor scans could be made. We then returned to the study of human neoplasms and selected an intravenous tracer dose of 100 µc of I131 HSA, scanning twenty-four hours after injection.