Background Patients with non-functioning pituitary macroadenoma (NFMA) currently have no established medical treatment options. Somatostatin analogues may decrease tumour size, but randomised trials are lacking. In vivo somatostatin receptor assessment with ⁶⁸Ga-DOTATATE PET could help in selecting patients for treatment. We aimed to determine the effect of the somatostatin analogue lanreotide on tumour size in patients with a ⁶⁸Ga-DOTATATE PET-positive NFMA.

Methods The GALANT study was an investigator-initiated, multicentre, randomised, double-blind, placebo-controlled, phase 3 trial performed in the Netherlands and funded by Ipsen Farmaceutica BV. We included adult patients with a suprasellar extending NFMA, either surgery-naïve or postoperative remnant. Important exclusion criteria were previous sellar radiotherapy and use of dopamine receptor agonists. Somatostatin receptor expression in the NFMA was determined by ⁶⁸Ga-DOTATATE PET/CT, co-registered with MRI. A predefined sample of 44 PET-positive patients were randomly assigned to lanreotide 120mg (n=22) or placebo (n=22) subcutaneous injections every 28 days for 72 weeks. The primary outcome was change in cranio-caudal tumour diameter.

Results  49 patients were included in order to randomise 44 patients. The mean (SD) change in cranio-caudal tumour diameter was +1.2 (2.5) mm with lanreotide and +1.3 (1.5) mm with placebo; ANCOVA adjusted mean difference vs placebo –0.1 mm (95% CI -1.3 to 1.2, p=0.93). Study treatment was completed in 13 (59%) lanreotide and 19 (86%) placebo participants. Withdrawal due to tumour progression occurred in three lanreotide and three placebo participants. Four participants in the lanreotide group withdrew due to adverse events and two due to other reasons. Adverse events occurred in 22 (100%) lanreotide and 21 (95%) placebo participants; gastrointestinal complaints were most common. There were no treatment-related serious adverse events.

Conclusion Compared with placebo, lanreotide treatment did not reduce tumour size or growth in ⁶⁸Ga-DOTATATE PET-positive NFMA patients.