Influence of lanreotide on uptake of 68 Ga-DOTATATE in patients with neuroendocrine tumours: a prospective intra-patient evaluation.

INTRODUCTION: Somatostatin receptor imaging with PET is the standard of care for patients with a neuroendocrine tumour (NET). Since therapy and imaging with somatostatin analogues utilize the same receptor, current guidelines recommend withdrawing long-acting somatostatin analogues for 3-4 weeks prior to somatostatin receptor PET imaging. The aim of this study is to prospectively assess the effect of lanreotide use on the uptake of 68 Ga-DOTATATE intra-individually 1 day prior to and 1 day post injection of lanreotide.

METHODS: Thirty-four patients with metastatic and/or unresectable NET and currently on lanreotide therapy for at least 4 months were included in the study. A 68 Ga-DOTATATE PET/CT scan was performed on the day before and the day after lanreotide injection. In each patient 68 Ga-DOTATATE uptake (SUVmax , mean , peak ) was assessed in both tumour lesions and normal tissue. All scans were assessed by two blinded nuclear medicine physicians for visual analysis. Paired T-tests were performed to determine the differences between the scans.

RESULTS: Of the 34 patients included, 31 were available for analyses in which 190 tumour lesions were measured. Uptake of 68 Ga-DOTATATE in tumour lesions was increased significantly after lanreotide, but decreased significantly in the liver, spleen, and thyroid gland resulting in a higher tumour-to-liver ratio.

CONCLUSION: Lanreotide injection prior to 68 Ga-DOTATATE PET/CT does not result in decreased tumour uptake. In contrast, tumour uptake was increased, whereas the uptake in normal organs is decreased, leading to an increased tumour-to-liver ratio. However, these differences were small and not deemed clinically relevant. These results strongly suggest that discontinuation of lanreotide injections in the weeks prior to 68 Ga-DOTATATE PET examinations is unnecessary and does not compromise nuclear medicine imaging results.