ORIGINAL ARTICLE Safety of multiple repeated cycles of 177 Lu-octreotate in patients with recurrent neuroendocrine tumour Anna Yordanova 1 & Karin Mayer 2 & Peter Brossart 2 & Maria A. Gonzalez-Carmona 3 & Christian P. Strassburg 3 & Markus Essler 1 & Hojjat Ahmadzadehfar 1 Received: 29 October 2016 /Accepted: 8 February 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract Purpose Peptide receptor radionuclide therapy (PRRT) is an effective therapy in patients with a somatostatin receptor- positive neuroendocrine tumour (NET). Still unclear is how many cycles of 177 Lu-octreotate can be repeated while main- taining an acceptable toxicity profile. The purpose of this study was to assess the safety of repeated PRRT in patients with recurrent NET. Methods We retrospectively evaluated data from 15 patients treated with repeated PRRT between 2004 and 2015. The medi- an administered activity was 63.8 GBq (range 52–96.6 GBq) in a median of 9 cycles (range 8–13 cycles). Nonhaematological and haematological toxicities were assessed from clinical reports and laboratory data. The rates of adverse events in three therapy groups were compared: during cycles 1 to 4, cycles 5 to 8, and cycles 9 to 13. Baseline laboratory assessments were also com- pared with data obtained at the end of treatment. The overall survival in the study patients was compared with survival data in patients who received only a baseline PRRT of three or four cycles. Results We observed no life-threatening adverse events (CTC-4) during 177 Lu-octreotate treatment. Reversible hae- matological toxicity (CTC-3) occurred in two patients (13%). No CTC-3/4 nephrotoxicity was recorded. More CTC-3 adverse events were recorded in the first therapy group than in the other two groups. Furthermore, there were no sig- nificant changes in the mean values of thrombocytes, leucocytes and serum creatinine before and after therapy. However, the mean haemoglobin levels fell from 14 g/dL to 11 g/dL. Finally, compared with those patients who received three or four cycles, there was a survival benefit in patients treated with repeated PRRT (censored overall survival 85.6 vs. 69.7 months, p < 0.001). Conclusion Therapy with eight or more cycles of 177 Lu- octreotate was well tolerated and led to a survival benefit in patients with recurrent NET. Keywords PRRT . 177 Lu-octreotate . Neuroendocrine tumours . Relapse therapy Introduction The therapeutic target of peptide receptor radionuclide therapy (PRRT) with 177 Lu-octreotate in neuroendocrine tumours (NET) is the overexpression of somatostatin receptors (SSTR). Importantly, 177 Lu-octreotate shows a high affinity for the most frequent receptor subtype, SSTR 2 [1]. 177 Lu- octreotate has been shown to be especially effective in patients with slow-growing, well or moderately differentiated NET (grade1/2) [2–8]. NETTER-1 is the first randomized phase III trial which recently showed a clear benefit of PRRT in patients with advanced midgut NET. The study indicates that this therapy is a promising option as first-line treatment for advanced NET [2]. Another advantage of PRRT is its moderate toxicity. Several studies have shown good tolerability regarding renal function [4, 6, 8–12] and haematopoiesis in patients [4, 6, 8–10, 12, 13]. PRRT could also be used in the salvage setting [10]. Although PRRT has been available for almost two * Hojjat Ahmadzadehfar hojjat.ahmadzadehfar@ukbonn.de 1 Department of Nuclear Medicine, University Hospital Bonn, Sigmund-Freud-Str. 25, 53127 Bonn, Germany 2 Department of Internal Medicine 3, University Hospital Bonn, Bonn, Germany 3 Department of Internal Medicine 1, University Hospital Bonn, Bonn, Germany Eur J Nucl Med Mol Imaging DOI 10.1007/s00259-017-3652-1