Role of 131I-metaiodobenzylguanidine (MIBG) in the treatment of neuroendocrine tumours. Experience of the National Cancer Institute of Milan.

Background: 45 patients with neuroendocrine tumours (22 neuroblastomas, 10 phaeochromocytomas, 3 para-gangliomas, 6 medullary thyroid carcinomas and 4 carcinoids) underwent 131I-MIBG therapy.

Methods: All patients, with the exception of 5 phaeochromocytoma cases with nonoperable disease, had previously been treated with conventional therapies. Patients had a previous diagnostic scintigraphy with 131I-MIBG (activity 20-44.4 MBq) or with 123I-MIBG (activity 74-222 MBq). The therapeutic activity for adults ranged from 3.7 to 7.4 GBq of 131I-MIBG; for children from 2.7 to 5.5 GBq. All treatments were repeated at not less than 4-weekly intervals. The neuroblastoma patients were divided into two groups: the first included 14 patients with advanced metastatic disease not responding to previous treatments; the second included 8 patients with documented residual neuroblastoma tissue that could not be surgically removed after first-line therapy.

Results: In neuroblastoma patients with advanced disease resistant to previous therapies 2 out of 14 showed a partial response, 9 stable disease and 3 progression of cancer. In neuroblastoma patients with residual disease (7 evaluable out of 8) we obtained 3 partial responses; a stable response was observed in 3 patients. The results of MIBG therapy in the group of phaeochromocytoma patients (9 evaluable out of 10) consisted of 3 partial responses, 5 stable disease and 1 progression. Evaluation of the response carried out on the basis of biochemical parameters increased the responses and MIBG therapy showed good effectiveness in controlling the functional symptoms. In the group of paraganglioma patients we observed 1 complete, 1 partial and 1 stable response. In patients with medullary thyroid carcinoma a partial response was observed in 1 patient with mediastinal metastases and 2 disease stabilisations were seen in another 2 patients. Patients with carcinoids who underwent MIBG therapy showed 3 disease stabilisations. The overall toxicity was acceptable, especially considering that the majority of our patients had had previous myelotoxic treatments (chemotherapy and/or radiotherapy, alone or in combination).

Conclusions: On the basis of our experience we can conclude that 131I-MIBG therapy is effective and also well tolerated.