Use of /sup 125/I as a monoclonal antibody label for localizing human soft tissue sarcomas

Tumor specific IgG fragments labeled with /sup 125/I are commonly used for immunologic screening of monoclonal antibodies (Mab). When /sup 125/I-labeled mouse Mab 19-24 against a soft tissue sarcoma was injected into patients (Pts) with metastatic disease, external probe surveys localized sites of known metastasis. The question of feasibility of metastatic imaging with I-125 was raised and investigated. 11 Pts with biopsy proven metastasis and 5 suspected but found disease free subsequently were imaged. Each received 300 μg of Mab 19-24 (corresponding to 250 μCi I-125 in 10 pts and 500 μCi in 6 pts) diluted in 50cc 5% HSA. Gamma camera had 1/4'' crystal, 10'' diameter and capability of selecting a 20% window symmetrically bracketed over the 35 KeV peak. Serial imaging included anterior abdomen, anterior and posterior chest and any other suspected areas of recurrence. The first set of images were obtained for 10 K cts or 10 min whichever occured first. Follow up images were taken for the corresponding same duration in order to facilitate washout evaluation. In five pts nonspecific /sup 125/I Mab-P/sub 3/ was also administered several days before or following the specific antibody imaging. Correlative imaging procedures were performed on all patients. Optimum tumor/background visualization occurred between 24-48 hours. Lesions were detected in 10 of 11 biopsy proven pts (sens. = 91%). Smallest lesion detected was 1 x 1.5 cm in the groin area. No lesions were detected in 5 tumor free pts (spec. = 100%). With suitably specific Mab, proper equipment and proper imaging protocol, I-125 Mab can provide diagnostically useful images