Intrapatient and interpatient comparison of tumor size and monoclonal antibody uptake in melanoma

In two panels totaling 52 patients with melanoma who were imaged with In-111 labeled 96.5 or ZME-018 (ZME) monoclonal antibodies (MoAb), four patients demonstrated numerous metastases (greater than or equal to 20) in the subcutaneous tissues and peripheral lymph nodes. These constituted four intrapatient groups of tumors. These were selected for an intrapatient comparison of tumor size and uptake. Data on 16 additional patients imaged with 96.5 MoAb with fewer (less than or equal to 11) such tumor foci were pooled and used as an interpatient control group of tumors. Uptake was graded 0-5+ (liver = 4+). The data were similar in all five groups. All tumors with a diameter less than 0.7 cm were not detected. All large tumors were demonstrated, usually with high uptake. Small tumors (greater than or equal to 0.7 cm in diameter), however, showed variable uptake, from 0-4+. Thus, tumors within one patient were as variable in uptake as tumors between patients. Immunologic studies of melanoma tumor antigens have shown a similar variability. It is suggested that antigenic heterogeneity is responsible for the variable scintigraphic demonstration of such tumors.