The value of radiolabelled MIBG and octreotide in the diagnosis and management of neuroendocrine tumours

Neuroendocrine tumours have a particular tendency to express functional receptors and/or uptake mechanisms. Radionuclides, such as I-123-MIBG, which is taken up by a specific uptake mechanism, and In-111-pentetreotide, which binds to somatostatin receptors, present an imaging modality based on these physiological characteristics rather on purely anatomical alterations. They have been successfully utilised for both the diagnosis and staging of neuroendocrine tumours, as they can identify lesions beyond the diagnostic sensitivity of conventional imaging modalities. Scintigraphy with In-111-pentetreotide is in general more sensitive but scintigraphy with I-123-MIBG may occasionally demonstrate lesions not evident with In-111-pentetreotide. Although both are effective in identifying hepatic metastases there may be quantitative and qualitative differences in the pattern of uptake. I-131-MIBG therapy, based on a positive I-123-MIBG scan, produces symptomatic and hormonal improvement and moderate tumour regression/stabilisation in many patients with metastatic neuroendocrine tumours with minimal adverse effects. It may be a valuable alternative or additional therapeutic option to the currently available conventional treatment modalities. Although experience with Y-90-DOTA-D-Phe(1)-Tyr(3)-octreotide therapy is still limited, preliminary studies have demonstrated useful activity in tumours with positive In-111-pentetreotide scans, and yet other radionuclide analogues may become available. However, treatment with the combination of both radionuclides is another therapeutic possibility.