Mechanism of action of octreotide in acromegalic tumours in vivo using dynamic contrast-enhanced magnetic resonance imaging.

CONTEXT

Octreotide causes significant tumour shrinkage in patients with acromegaly but the exact mechanism of action is unclear in vivo.

OBJECTIVE

To determine the mechanism of action of octreotide in vivo using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

DESIGN

Five patients with acromegaly were treated with octreotide as primary medical therapy. DCE-MRI was done at baseline and 24 weeks. Local ethical committee approval was granted.

SETTING

Study was done in a tertiary care centre.

PATIENTS

Five patients with newly diagnosed acromegaly were recruited.

INTERVENTION

Patients were started on subcutaneous octreotide and DCE-MRI was done on 0 and 24 weeks.

MAIN OUTCOME MEASURES

Amplitude of contrast intake, exchange rate and maximum enhancement index of tumour tissue was compared before and after treatment.

RESULTS

Amplitude of contrast intake (9.87 +/- 3.52 vs. 4.97 +/- 1.96 P < or = 0.05) and exchange rate (6.27 +/- 1.57 vs. 1.63 +/- 0.76 P value < or = 0.01) were significantly higher at baseline in adenoma compared to normal pituitary tissue but was comparable to normal pituitary tissue after treatment. There was a significant decrease in amplitude of contrast intake and exchange rate which relates to functional vascularity of adenoma at 24 weeks compared to baseline (P-values 0.026 and 0.002 respectively) but there were no significant changes in the normal pituitary tissue.

CONCLUSION

DCE-MRI in acromegalic tumours treated with octreotide showed a significant reduction in functional vascularity after octreotide therapy compared to baseline in pituitary adenomas. This supports the antiangiogenic action of somatostatin analogue therapy in vitro, but it remains unclear if this mechanism is important clinically in analogue pre-treatment reducing the effect of radiotherapy on these pituitary tumours.