Relationship Between Best Tumor Shrinkage and Progression-Free Survival and Overall Survival in Patients With Progressive Midgut Neuroendocrine Tumors Treated With [177Lu]Lu-DOTA-TATE: Ad Hoc Analysis of the Phase III NETTER-1 Trial

Abstract

Background

In many solid tumors, early tumor shrinkage predicts the durability of treatment response. It is unclear whether this is the case for neuroendocrine tumors treated with peptide receptor radionuclide therapy (PRRT).

Methods

Data from the phase III NETTER-1 study of [¹⁷⁷Lu]Lu-DOTA-TATE (¹⁷⁷Lu-DOTATATE) for the treatment of advanced, well-differentiated, midgut NETs were used to investigate whether objective tumor shrinkage (local review) with ¹⁷⁷Lu-DOTATATE is associated with progression-free survival (PFS) and overall survival (OS) duration.

Results

Overall, 117 patients were treated with ¹⁷⁷Lu-DOTATATE (four cycles of 7.4 GBq every 8 weeks). In a landmark analysis, best tumor shrinkage from baseline until data cut-off (prior to first progression) was not associated with PFS (n = 102; hazard ratio: 1.002 [95% confidence interval (CI): 0.99–1.02]; nominal p = 0.7808). In further ad hoc analyses, patients on the ¹⁷⁷Lu-DOTATATE arm were dichotomized into ≥ 30% tumor shrinkage from baseline (18/117 [15.4%]) and < 30% shrinkage (99/117 [84.6%]). Median (95% CI) PFS was 17.6 (16.5–30.3) months in the ≥ 30% shrinkage group and 25.0 (19.4–31.0) months in the < 30% group. OS was not significantly different for the two tumor shrinkage groups (not estimable [31.0 months–not estimable] and 44.3 [34.9–53.8] months, respectively).

Conclusions

These results suggest the benefit of PRRT and the potential PFS and OS benefit of ¹⁷⁷Lu-DOTATATE should not be based on tumor shrinkage (objective response versus stable disease) and that lack of tumor shrinkage should not impact application of the approved four cycles of ¹⁷⁷Lu-DOTATATE.