Indium-111-labeled B72.3 monoclonal antibody in the detection and staging of breast cancer: A phase I study

Sixteen patients with primary breast cancer were studied with a pancarcinoma monoclonal antibody B72.3, an IgG₁ molecule directed against tumor-associated glycoprotein (TAG-72) present in several tumors. Five millicuries of ¹¹¹In was used to label 0.2 mg (six patients), or 2 mg (six patients), or 20 mg using the site-directed bifunctional DTPA method (at carbohydrate moiety). Digital, planar, and SPECT images were obtained at 2, 48, 72 and 96 hr when possible. HAMA levels were obtained before the Mab infusion and at 1, 3, and 6 wk postinfusion. Fourteen of 14 known primary breast lesions were detected by imaging (100% sensitivity). Two fibrocystic lesions were negative. Seven of 14 patients had lymph node metastases by histologic methods, but all were missed by radioimmunoscintigraphy. Tumor uptake of Mab ranged 0.00054%-0.0038% of the ID/g. The tumor-to-normal breast tissue ratio was 4.3 ± 0.91 (mean ± s.e.m.). Lymph nodes localization of ¹¹¹In-B72.3 by tissue analysis was similar for tumor-bearing and normal nodes (0.0039 ± 0.0023 versus 0.0025 ± 0.0019). Pharmacokinetics revealed mean plasma half-life of 33.3-41.2 hr for the different doses. There was no statistical difference between any of the pharmacokinetic parameters of different doses. HAMA was positive only in 17% of the patients. The study suggests that this antibody has 100% sensitivity for primary breast cancers, but very poor detection rate of metastatic lesions in axillary lymph nodes; thus making it of questionable value in the initial staging process of this disease.