Streptozotocin Therapy for Malignant Pheochromocytoma-Reply

—The interesting report of Gross et al certainly reinforces the fact that not all tumors of a given type will respond to an antineoplastic drug. I noted in the comments of my report that "It is also possible that it is not the difference in dose schedule but that some, but not all, patients with malignant pheochromocytomas have tumors that are sensitive to the drug (streptozotocin)."¹

At the present time I cannot completely concur with Gross et al's comment "... that first line treatment, in appropriate cases, might be the recently reported radioiodinated norepinephrine analogue MIBG (meta-iodobenzylguanidine)...." In a recent report only two of five patients with malignant pheochromocytomas showed a significant clinical response to therapy with MIBG labeled with iodine 131.² In order for a malignant pheochromocytoma to concentrate and retain MIBG ¹³¹I it is likely that the tumor will have to have an active neuronal pump