All subjects in Group A will be treated in an induction stage using 10-14 week dosing for up to 4 treatments. If an individual patient shows stable or improving disease status with no significant toxicities after the 4 induction treatments, they will be assessed 12-20 weeks after the last therapeutic treatment for entry into the maintenance stage. Patients will be re-assessed for stable or improving disease status with no significant toxicities 12-20 weeks after the last treatment of each cycle (1 cycle = 2 treatments at 22-40 week intervals) of the maintenance stage for consideration of further maintenance cycles (re-evaluations), up to a maximum of 4 cycles per patient if there have been no significant toxicities or progression. At each treatment, an amino acid solution is infused prior to and during the Lu-DOTA-TATE infusion to protect the kidneys. Subjects will be followed for 6 months and 1 year (± 4 weeks) following their last treatment dose to determine progression-free survival. All subjects meeting evaluation criteria will be analysed for safety, and all Group A subjects who have received at least two treatments of Lu-DOTA-TATE will be evaluated for efficacy (progression free survival and effect on Quality of Life). Those Group B subjects with adequate baseline data for comparison collected retrospectively from a chart review study (REV-LUT-001) may also be evaluated for safety and efficacy. Additional optional characterization of tumour samples from subjects who have had surgery before or during the study may be performed to characterize NET tumour biology changes following Lu-DOTA-TATE treatment.