Breast cancer imaging with mouse monoclonal antibodies

The localization of 111In-labelled MA5 monoclonal antibody, reactive with a breast tumor associated antigen, was studied in 17 patients. MA5 was selected because 1) it reacts with greater than 95% of primary and metastatic lesions, 2) the recognized antigen is present on the cell surface in vivo and 3) MA5 gives excellent localization in human breast tumor xenografts. Each patient received 2 mg antibody labeled with 5 mCi 111In and in some cases, 3 mg or 18 mg unlabeled carrier antibody. No serious allergic reactions were noted. There was a large uptake in the liver, less significant uptake in the spleen and bone, and minimal accumulation in the bowel. Bone lesions, primary tumors, soft tissue recurrences and lung metastases larger than 3 cm diameter were imaged, while only 1 lesion smaller than 3 cm was detected. Non specific accumulation of tracer was noted at the site of a port-a-cath, in a hematoma, in fibrocystic lesions, and at sites of previous radiation treatment. Extensive fibrosis and poor vascularization characteristic of breast tumors may explain in part the limited sensitivity of the imaging.