Treatment of malignant pheochromocytomas with 131-I metaiodobenzylguanidine and chemotherapy

Malignant pheochromocytomas have exhibited partial responses to treatments with 131-I metaiodobenzylguanidine (MIBG) and with chemotherapy. The author s combined these two therapeutic methods to determine if beneficial effects from each would be additive. Patients with documented malignant pheochromo cytomas were recruited with the intent of administering 131-I MIBG in three substantial amounts of radioactivity at 3-month intervals followed by a ye ar of chemotherapy in which cyclophosphamide, dacarbazine, and vincristine were to be given in 21-day cycles. Six patients entered the protocol. After the 131-I MIBG treatments, three patients manifested declines in the prese nce of tumor (smaller tumor volume or abnormalities on bone and 131-I MIBG scans) and the function of tumor (decreased rate of normetanephrine excreti on as the major index). Two patients completed at least 9 months of chemoth erapy and showed further reductions in the presence and function of tumors and were classified as having partial responses. Progressive disease afflic ted three of the other four subjects. Even though toxicity was minimal from 131-I MIBG, it was sufficient to force reduction in the dosages or duratio n of chemotherapy. A combination of 131-I MIBG treatments and chemotherapy produced additive effects in reducing malignant pheochromocytomas. Toxicity moderately curtailed the proposed chemotherapy protocol.