Impact of the Ki-67 proliferation index on response to peptide receptor radionuclide therapy

Abstract

Purpose: The role of the Ki-67 tumour proliferation index (PI) in predicting the efficacy of peptide receptor radionuclide therapy (PRRT) in gastroenteropancreatic tumours (GEP-NET) remains undetermined. This single-centre analysis focused on the potential therapeutic impact of this immunohistochemical parameter.

Methods: A total of 81 consecutive GEP-NET patients treated with (177)Lu-DOTA-octreotate (mean activity of 7.9 GBq per cycle, usually four treatment cycles at standard intervals of 3 months) were retrospectively analysed. Both an evaluable PI and tumour response (modified SWOG criteria) were required for patient inclusion.

Results: Response of tumours with a PI of ≤20% (partial response 40%, minor response 15%, stable disease 34%, progressive disease 11%) was comparable in all PI subsets, including those with a PI of 20%. However, G3 tumours (PI > 20%) showed progression in 71% of patients.

Conclusion: Response to PRRT is consistent over the PI range of ≤20% (G1 + G2). Contrary to preliminary previous suggestions, a PI of 15% or 20% should not preclude candidates from somatostatin receptor-targeted radiotherapy.