Existing somatostatin-based radiotracers (e.g. 111In-DOTATOC) have sole affinity for somatostatin receptor subtype 2 (sst2). This represents a drawback, given that sst1–5 have been shown to be over-expressed in different tumours, alone or concomitantly [1]. Our goal, therefore, was to develop radiopeptides with broader receptor subtype profiles.

68Ga-DOTANOC is a first compound for PET imaging with high affinity for sst2 and sst5 [2]. Its affinity profile (IC50 nM) for human sst1–5 is, respectively, >10,000, 1.9±0.4, 40±5.8, 260±74 and 7.2±1.6. For comparison, the values for the standard compound, 111In-DOTATOC, are >10,000, 4.6±0.2, 120±26, 230±82 and 130±17.

figure a

Here we present the 60 min p.i. 68Ga-DOTANOC PET images and the 21 h p.i. 111In-DOTATOC planar images of a 52-year-old patient with an advanced neuroendocrine tumour. The two examinations were performed within 4 weeks. During this time interval the patient received bisphosphonates.

Preparation and application of 68Ga-DOTANOC PET and 68Ga-DOTATOC PET are comparable [3].

In the reported case study, the 68Ga-DOTANOC PET scan shows high radioligand uptake in the liver and bone metastases. Although many bone metastases appeared visually similar in the two scans, the right sixth rib and left occipital bone metastases (arrows) are much more visible on the 68Ga-DOTANOC PET scan. This selective difference cannot be explained simply by the advantages of the PET technique. The possible predominance of sst5 in these two bone metastases and the high sst5 affinity of 68Ga-DOTANOC are in fact the probable reasons for the high 68Ga-DOTANOC and low 111In-DOTATOC uptake. The enlarged liver and somatostatin receptor-positive organs such as the spleen (high uptake) and pituitary gland and thyroid (moderate uptake) are also visible. These normal organs, known to express more sst than just sst2, are better visualised with 68Ga-DOTANOC (see in particular the spleen).

We conclude that 68Ga-DOTANOC is an excellent candidate for primary diagnostic and follow-up investigations in patients with suspected or proven somatostatin receptor-positive tumours. Furthermore, in this case, predictive imaging indicates that 90Y- or 177Lu-DOTANOC has greater potential for treatment of this patient than 90Y- or 177Lu-DOTATOC.