Long-term palliation in metastatic carcinoid tumours with various applications of meta-iodobenzylguanidin (MIBG): pharmacological MIBG, 131I-labelled MIBG and the combination.

Carcinoid tumours are rare, but well known for their characteristic presentation with diarrhoea and flushes due to overproduction of serotonin in the case of liver metastases. Treatment is mainly based on the reduction of vasoactive peptide hypersecretion and symptomatic improvement Octreotide and interferon are widely applied and effective treatment options to induce symptomatic improvement and, to a lesser extent, biochemical response. The main drawbacks, however, are the need for frequent injections and/or the occurrence of side effects. A rather new approach is the application of meta-iodobenzylguanidine (MIBG), which resembles noradrenalin and serotonin. In carcinoid patients, MIBG is taken up in the tumour cells and stored in the neurosecretory granules. When labelled with 131 iodine, radionuclide imaging is positive in up to 70% of the patients. In these patients, two cycles of a therapeutic dose of radioactive MIBG may induce long-lasting palliation (8 months) by internal irradiation. Also, the non-radioactive MIBG compound may be effective in palliation, even in patients with a negative scan. The mode of action is based on specific tumour acidification as found in animal models, and/or based on its effect as a false neurotransmittor. Three case reports demonstrate different therapeutic possibilities of MIBG: 1) symptomatic relief with unlabelled MIBG, which is a safe and simple treatment; 2) the longterm palliation following radioactive treatment; and 3) an additional new aspect of predosing with unlabelled MIBG followed by radioactive MIBG led to improved tumour targeting and impressive clinical response.