Enhancement of I-131-MIBG uptake in carcinoid tumours by administration ofunlabelled MIBG

Iodine-131 metaiodobenzylguanidine (I-131-MIBG) has been used with success for the palliation of symptomatic, metastatic carcinoid tumours. However, o nly 70% of cases are MIBG-avid and tumour uptake is not always sufficient f or therapy. At The Netherlands Cancer Institute 34 carcinoid patients with no or insufficient uptake were treated with escalating doses of unlabelled ('cold') MIBG. No objective remissions were recorded, but a palliative effe ct (i.e. subjective disappearance of symptoms and/or reduction of medicatio n by more than 50%) was observed in 60% of cases (mean duration 4.5 months) . In 24 of the patients undergoing therapy with 'cold' MIBG, total body sci ntigraphy using 37 MBq I-131-MIBG was performed before and after infusion o f 'cold' MIBG. The biodistribution of I-131-MIBG and its tumour to non-tumo ur ratios were compared. After 'cold' MIBG the I-131-MIBG uptake in the sal ivary glands was suppressed in all patients, myocardial uptake in 21, and u ptake in normal liver tissue in 14. Pulmonary uptake was increased in 13 pa tients. More importantly, the tumour to non-tumour (T/NT) ratios improved i n 17 of the 24 cases (by 7.8-111.4% at 24 h). Of the initial six patients d emonstrating a significant increase in the T/NT ratio, five have subsequent ly received combined treatment of 7.4 GBq I-131-MIBG following the administ ration of 'cold' MIBG (both by 4 h intravenous infusion), resulting in a go od palliative response in four of them. These patients had previously been excluded from therapy with I-131-MIBG only. It is concluded that the admini stration of unlabelled MIBG may not only provide palliation to patients wit h carcinoid tumours, but may also alter the biodistribution of MIBG, enabli ng I-131-MIBG therapy to be used in cases not qualifying for this treatment due to insufficient tumour uptake. ((C) 2000 Lippincott Williams & Wilkins ).