The presence of somatostatin receptors in high density on tumor cells has led to the development of peptide receptor radiotherapy (PPRT) for NETs. Early studies with ¹¹¹In-, ⁹⁰Y-, or ¹⁷⁷Lu-labeled somatostatin analogues have reported promising results in the control of hormonally related symptoms.145 The earliest studies were carried out with [¹¹¹In-DTPA⁰] octreotide. Although symptomatic improvements were reported, objective tumor responses were rarely observed. Subsequently, ⁹⁰Y was linked to octreotide to create [⁹⁰Y-DOTA⁰,Tyr³] octreotide. Several studies were carried out in patients with NETs and produced response rates of 10% to 30%.145 In the largest prospective study that treated 90 patients with NETs, only a modest response rate of 4% was observed.146

Finally, a number of European centers are now using octreotate, which substitutes the C-terminal threoninol with threonine. Octreotate is linked to ¹⁷⁷Lu to create [¹⁷⁷Lu-DOTA0,Tyr3] octreotate. In the largest series, 504 patients with NETs were treated. Authors reported a response rate of 30% among a subset of 310 patients. However, if intent-to-treat analysis was performed, the objective response would be approximately 18%.147 In general, expected toxicities with peptide receptor radiotherapy include nausea, vomiting, abdominal pain, cytopenia, and hair loss. More serious side effects, including renal failure, leukemia, and myelodysplastic syndrome, have also been reported. Large-scale random assignment trials are needed to define its role in the management of pNETs ...