Does the modality of radionuclide treatment in NET have effect on PFS?

Objectives To determine if either I-131 mIBG or Y-90 DOTATATE therapy influenced progression free survival (PFS) in patients treated for disseminated neuroendocrine tumor (NET).

Methods A retrospective analysis was made in all patients (since 2005) treated with either I-131 mIBG or Y-90 octreotate (depending on the results of their functional imaging). The indication for treatment was radiological evidence for progressive disease as measured by CT in the 6 months prior to therapy. A standard treatment regime was either 3 cycles of 5.5-7 GBq I-131 mIBG or 3 cycles of 3-4GBq Y-90 DOTATATE at 10-12 week intervals. Early progression was determined by CT within 6 months of starting treatment. Median PFS was calculated from the date of first cycle until radiological progression was seen using RESCIST criteria.

Results Of the 37 patients given I-131 mIBG the median PFS for those 14 patients with evidence of progressive within 6 months on the CT was 7 months; significantly less (p<0.05) than the for those patients with disease stability or partial response at 6 months after first treatment where median PFS was 23 months. Likewise there were 74 patients who have completed treatment with Y-90 DOTATATE. The median PFS of the 27 patients with early progressive disease was 12 months which was significantly less (p<0.05) than the median PFS of 23 months in those with disease stability or partial response.

Conclusions The modality of treatment did not determine progressive free survival however early disease progression suggested poor prognosis in both treatment groups