Long-term effects of lanreotide SR and octreotide LAR on tumour shrinkage and GH hypersecretion in patients with previously untreated acromegaly.

BACKGROUND AND OBJECTIVE: The therapeutic efficacy of lanreotide SR and octreotide LAR has been studied widely in patients treated previously with neurosurgery and/or radiotherapy. These therapies limit the evaluation of the long-term effects of somatostatin analogues on tumour shrinkage. Neurosurgical and radiotherapy treatments cause irreversible anatomical changes in pituitary morphology, which can make accurate evaluation of tumour shrinkage difficult. The aim of this study was to investigate the therapeutic efficacy of lanreotide SR and octreotide LAR in previously untreated patients with acromegaly. We aimed to investigate the long-term effects of these drugs on tumour shrinkage and growth hormone (GH) hypersecretion without the confounding influences of previous therapy.

PATIENTS AND METHODS: Twenty-three newly diagnosed patients with acromegaly (14 women, nine men) with active disease began the study; of these, three were lost for follow-up, leaving a total of 20 patients to complete the study. Patients were assigned randomly to lanreotide SR (12 patients) and octreotide LAR (eight patients), and the randomization stratified patients to assure a balance between the groups with respect to baseline tumour dimension, age and sex. Tumour volume was evaluated by magnetic resonance imaging of the sella, and calculated with the rotating ellipsoid formula. A morphological and biochemical evaluation was performed at baseline, 12 and 24 months after beginning lanreotide SR and octreotide LAR treatment. A reduction of tumour volume of at least 10% was considered significant.

RESULTS: Biochemical control increased progressively throughout the study in patients with microadenomas more than in patients with macroadenomas (70% vs. 10%; P < 0.05) and without a difference between lanreotide SR and octreotide LAR (41.0% vs. 37.5%; P not significant). After 12 months of treatment, mean tumour shrinkage was 28.3 +/- 18.0%. A greater reduction was observed in macro- vs. microadenomas (40.5 +/- 17.0% vs. 16.1 +/- 8.0%, respectively; P < 0.05). No statistical difference in the tumour shrinking effects of lanreotide SR vs. octreotide LAR was observed (26.5 +/- 17.3% vs. 31.1 +/- 16.1%, respectively). At the 24th month of therapy, no further overall shrinkage was observed, compared to the 12-month evaluation (31.9 +/- 17.2% vs. 28.3 +/- 18.0%) at which there was no difference between lanreotide SR and octreotide LAR (30.0 +/- 17.2% vs. 34.8 +/- 16.5%, respectively).

CONCLUSIONS: This study showed that the new long-acting somatostatin analogues, lanreotide SR and octreotide LAR, cause significant shrinkage of pituitary GH-secreting adenomas in previously untreated patients with acromegaly. This effect was more marked in macroadenomas than microadenomas, and did not correlate with control of GH hypersecretion.