Interferon and meta-iodobenzylguanidin combinations in the treatment of metastatic carcinoid tumours.

Interferon (IFN) and meta-iodobenzylguanidin (MIBG) are active in metastatic carcinoids. In a phase II study, we evaluated the effect upon diagnostic 131I-MIBG uptake and the clinical response of the combination. 131I-MIBG scintigraphy was performed prior to treatment, after 8 weeks of IFN and after unlabelled MIBG. The tumour over non-tumour (T/NT) ratios were quantitatively determined by comparing counts in the centre of the tumour (liver metastases) with those in an adjacent area of normal liver uptake (T/NT1) and with abdominal background area (T/NT2). The T/NT1 ratio showed an increase of >10% in only four out of 21 patients (19%) after IFN (P = 0.178) and significantly more often in nine out of 18 patients (50%) after unlabelled MIBG (P = 0.016). The absolute uptake in tumour deposits was also increased if compared with the abdominal background (T/NT2: 23% increase after IFN and 83% increase after unlabelled MIBG). The combination produced 91% of patients with stable disease (using World Health Organisation criteria) at computed tomography scan and a biochemical response (a reduction of at least 50% in urinary 5-hydroxyindolacetic acid excretion) in 39%. IFN-alpha did not significantly improve tumour retention of 131I-MIBG. In contrast, unlabelled MIBG significantly improved biodistribution and tumour uptake in 83%. A synergistic effect was not seen.