Background Clinically non-functioning pituitary macroadenomas (NFMA) have been reported to express somatostatin receptors (SSTR), but results are inconsistent across different studies. This may be related to limited sensitivity and specificity of techniques used to date, i.e. immunohistochemistry in surgical specimens and 111In-DTPA-octreotide scintigraphy in vivo. The aim of this study was to assess SSTR expression in NFMA in vivo using 68Ga-DOTATATE PET, which offers superior sensitivity and spatial resolution as compared to planar scintigraphy or SPECT.
Methods Thirty-seven patients diagnosed with NFMA underwent 68Ga-DOTATATE PET/CT of the head in the framework of a randomised controlled trial assessing the effect of the somatostatin analogue lanreotide on NFMA size (the GALANT trial). Individual co-registered T1-weighted pituitary MRIs were used to assess 68Ga-DOTATATE uptake. A circular region of interest was placed within the adenoma and the mean standard uptake value (SUVmean) was evaluated. An SUVmean of >2 was considered positive.
Results 68Ga-DOTATATE uptake was positive in 34/37 patients (92%), with SUVmean in positive adenomas ranging from 2.1 to 12.4 (mean±SD: 5.8±2.6).
Conclusions This is the first report of 68Ga-DOTATATE PET performed in NFMA patients, demonstrating in vivo SSTR expression in the vast majority of cases. The high positivity rate when compared to results obtained with 111In-DTPA-octreotide scintigraphy probably reflects the superior sensitivity and resolution of PET imaging. Its clinical use in the prediction of response to somatostatin analogues will be evaluated in the GALANT trial.
Trial registration: Netherlands Trial Register, NL5136, registered 18 August 2015, https://www.trialregister.nl/trial/5136; and EudraCT, 2015-001234-22, registered 10 March 2015, https://eudract.ema.europa.eu/