Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE in Advanced Neuroendocrine Tumours (NETs) in a Limited Resource Environment

Background We decided to evaluate the clinical ecacy and safety of peptide receptor radionuclide therapy (PRRT) with 177-DOTATATE in patients with neuroendocrine tumors (NETs). Sixteen patients with pathologically veried NETs including eight females and eight males were enrolled in this study. Before PRRT for evaluation of somatostatin receptor expressing, the patients underwent 68Ga-DOTATATE PET-CT or 99mTc-octreotide scintigraphy. The treatment response was assessed according to the response evaluation criteria in solid tumors (RECIST) which was classied into complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD). In addition, for evaluation of toxicity, monthly blood analysis was performed including hematology, renal function (creatinine), liver status. The Eastern Cooperative Oncology Group (ECOG) status performance was applied for estimating the patients’ general condition including 0 (fully active) to 5 (dead). In addition, overall survival (OS) was calculated as the time interval between start of PRRT to death from any reason. Cooperative Oncology Group (ECOG) status performance was applied for estimating the patients’ general condition including 0 (fully active) to 5 (dead). ECOG was assessed before each PRRT session and at least three months after the nal treatment session in the follow-up visit for evaluation of change in QOL.


Introduction
Neuroendocrine tumors (NETs) de ned as neoplasms originated from cells of the nervous systems and endocrine (hormonal). According to the data from the National Cancer Institute, it has been seen an increased incidence rates of (NETs) (0.3 per 100000) that is contributed with progressed professional diagnostic tools [1].
For treatment of NETs, based on tumor condition, several treatment methods are available which the surgery is rst line, even in the metastasized tumors. In the nonresectable tumors, several palliative therapeutic options have been used including chemotherapy and radionuclide therapy [2].
An exclusive properties of NETs is overexpression of somatostatin receptors (SSTRs) leading to establishment of alternative therapeutic option for these tumors including radiolabeled somatostatin analogues [3].
Nowadays, peptide receptor radionuclide therapy (PRRT) is developed as systematic administration of radiolabeled somatostatin analogues with radiopharmaceuticals such as 177Lu-DOTA0-Tyr3-octreotate (177Lu-DOTATATE) to molecularly targeted malignant NETs. There are several studies about the clinical e cacy of PRRT with 177Lu-DOTATATE in NETs demonstrated the long-term survival for these patients [1,4,5]. Nevertheless, the PRRT approach has demonstrated low or reversible side effects on kidneys function and bone marrow that introduced as dose-limiting organs [6].
Many studies have con rmed promising results of 177Lu-labeled PRRT for treatment of these patients through gamma and beta emission as theranostic agent [2,7,8]. The purpose of this study is to evaluate the clinical e cacy and safety of PRRT with 177Lu-DOTATATE in patients with NETs and impact of this therapy on overall survival and quality of life (QOL).

Treatment
For PRRT, the patients were hospitalized in the dedicated theranostics center of Department of Nuclear Medicine. In each PRRT cycle, the patients received 3.7 to 7.4 GBq of 177Lu-DOTATATE. Commercial radiolabeled 177Lu-DOTATATE was obtained from Pars isotope co., Iran.
Before administration of 177Lu-DOTATATE, renal side effect was decreased through intravenously injection of amino acid solution (2.5% arginine and 2.5% lysine, 1 L) which was started 30 minutes before infusion of the radiopharmaceutical. After that, the radiopharmaceutical was injected intravenously during about 20 minutes.
The time interval between treatment cycles were 6-8 week. The treatment was considered unsuccessful and subsequently stopped if there were complications, disease progression, inability or unwilling of patient to participate and death.

Post-treatment Imaging
For evaluation of radiotracer distribution, scintigraphy was performed at 24 and 48 hours after PRRT. Images were acquired with a dual-head gamma camera (Vertex ADAC plus) equipped with low energy high resolution collimator and the energy was set on 113 KeV with energy window of 20%. The scan was performed in whole body and SPECT if needed.

Response Evaluation
The tumor morphological assessment and treatment response evaluated through follow-up imaging including CT scan, MRI every 6-8 weeks during treatment cycles as well as 3 and 6 months after the lost treatment session and assessed according to the response evaluation criteria in solid tumors (RECIST)[9].
According to RECIST, the treatment response was classi ed into complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD). Also, if available, some patients performed 68Ga-DOTATATE PET/CT for follow-up in addition to anatomical imaging. The Eastern Cooperative Oncology Group (ECOG) status performance was applied for estimating the patients' general condition including 0 (fully active) to 5 (dead). ECOG was assessed before each PRRT session and at least three months after the nal treatment session in the follow-up visit for evaluation of change in QOL.
In addition, overall survival (OS) was calculated as the time interval between start of PRRT to death from any reason.

Data collection and Statistical Analysis
The disease-related data were obtained from our hospital and another clinical department. The descriptive and categorial data were expressed as median and frequency, respectively. For analyzing of categorial variables, Chi-square test was used. For evaluating OS and the impact of multiple parameters on OS, the Kaplan-Meier estimator and log-rank tests were used. Statistical analysis was performed using SPSS Statistics 21 (IBM Corporation, Somers, NY, USA). Pvalue of less than 0.05 was considered statistically signi cant.

Response Rate
At the end of data collection, 11/16 patients had PR, 2/16 showed CR, 1/16 showed SD and 2/16 showed PD according to the RECIST. In addition to anatomical imaging, 4 patients performed follow-up 68Ga-DOTATATE PET/CT which was in correlation with results of anatomical imaging. 3 patients were expired during and after the PRRT period time. Before PRRT, the medians of ECOG and KPS were 1.5 and 75 which after treatment were, signi cantly, improved to 1 and 80, respectively (p<0.05). according to the Kaplan-Meier test, the median of OS was estimated 23 months (95%CI:7.90-38.09) ( gure 1). We found no signi cant difference concerning OS in comparison with other factors including baseline ECOG, sex, krenning score, tumour site, metastases, previous therapy, number of PRRT cycle, total administered dose and PRRT related toxicity (p<0.05).

Side Effects
In evaluation of PRRT related toxicity according to the CTCAE, 3 patients showed grade I and 3 other showed grade II leucopenia. Furthermore, 3 and 7 patients had grade II and grade I anemia, respectively. Serum creatinine in 3 patients increased to grade I. In addition, 2 patients showed grade I thrombocytopenia ( Table 2).

Discussion
In this study, we reported our 4 years' experience in PRRT with 177Lu-DOTATATE in patients with NETs. We evaluated the clinical e cacy and safety of PRRT in 16 patients with NET.
In the recent decades, after it has been demonstrated that NETs can be detected with radiolabeled somatostatin analogues such as 68Ga-DOTATATE PET/CT and 99mTc-octreotide, PRRT has been introduced as a therapeutic option for NETs, especially in patients who were refractory or progressive to conventional therapeutic modalities such as surgery, somatostatin analogues therapy and chemotherapy. From time of introducing, several studies have been performed for evaluation of clinical e cacy and safety of PRRT [2,3,7,8,[10][11][12][13]. In a phase 3 trial, e cacy and safety of 177Lu-DOTATATE therapy in advanced and progressive midgut NETs in comparison with somatostatin analogues therapy (control group) had been evaluated which resulted in 18% response rate in PRRT group in comparison with 3% in the control group. In the evaluation of survival, 14 and 26 death occurred in the PRRT and control group, respectively. [12]. In another study, e cacy of PRRT with 90Y-or 177Lu-DOTANOC as another somatostatin analogue had been evaluated in patients with NET which revealed moderate toxicity in 8/20 patients. In addition, of 20 patients underwent PRRT, a partial remission was found in 5 patients, stable disease in 11 patients, and tumor progression in 4 patients [2].
In our study, according to RECIST, of 20 evaluated patients, PR was found in 11, CR in 2, SD in 1 and PD in 2 patients which demonstrated favorable e cacy of PRRT in treatment of patients with NET. In concordance to our results, E. Abou Jokh Casas et al reported effectiveness of PRRT in 69% of patients with NETs. However, they reported progression in 25% of patients [7]. Dik J. Kwekkeboom et al evaluated effectiveness of PRRT with 177Lu-octreotide as a radiolabeled somatostatin analogue in patients with metastasized or inoperable endocrine gastroenteropancreatic tumors that resulted in among 131 treated patients, CR in 2%, PR in 26%, minor response in 19%, SD in 35% and PD in 18% of patients [3]. Also, in another study, they evaluated e cacy of 177Luoctreotide in larger group of patients with gastroenteropancreatic neuroendocrine tumors. They reported that of 310 treated patients, CR was observed in 2%, PR in 28%, minor response in 16%, SD in 35% and PD in 20% of patients [13]. It should be mentioned that these results compare favorably to chemotherapy reports in these patients. Previous studies showed PR and CR in less than 20% of patients. In addition, PRRT showed better outcome than chemotherapy in OS, duration of the response and toxicity [14][15][16].
In this study, we evaluated physical condition and change in QOL of patients with assessment of KPS and ECOG scores. Our results indicated that after treatment, KPS and ECOG were signi cantly improved compared to before treatment which revealed improvement in QOL of treated patients. In concordance with our results, Saima Khan et al evaluated QOL of patients with NETs underwent PRRT with 177Lu-octreotide in different aspects including KPS. They reported that after PRRT overall QOL signi cantly improved. In addition, in evaluation of KPS, they indicated that KPS signi cantly improved in patients responded to PRRT and deteriorated in patients progressed after PRRT [17]. In another study, QOL was assessed with EORTC QLQ-C30 questionary completed after each cycle of PRRT indicated overall QOL was signi cantly improved after PRRT. In analyzing speci c aspects of QOL, they reported signi cant improvement in emotional functioning, pain and diarrhea [18].
The median OS in this study was 23 months for all patients and death occurred in 18% (3/16) of patients. There was no signi cant difference concerning OS compared to several baseline characteristics of patients which may be due to the small sample size and low number of events. Abou Jokh Casas E et al reported that several factors can affect the OS after PRRT with 177Lu-DOTATATE in patients with metastatic NETs including toxicity in previous treatment, tumor grade and presence of bon lesions [7]. In another study, it has been shown that in patients with grade 1 and 2 gastroenteropancreatic NET, PRRT resulted favorable response and long term outcome indicated that tumor grade is the most powerful predictive factor in OS [19].
According to the CTCAE, in this study, approximately 75% of patients developed PRRT related toxicity. Most common toxicity was anemia which occurred in 10/16 patients including grade 2 in 3 and grade 1 in 7 patients. Leucopenia developed in 6 including grade 2 in 3 and grade 1 in 3 patients, nephrotoxicity of grade 1 in 2 and thrombocytopenia of grade 1 in 2 of patients. In a study, it has been reported that during PRRT, hematological toxicity had been observed in 38.8% of patients [7]. A multicenter study evaluated 450 patients with NETs, it has been revealed that PRRT has rare serious adverse events including leukopenia of grade 3 in 1.1% and thrombocytopenia of grade 3 in 1.3%, and grade 4 thrombocytopenia was observed in only one patient [20].
This study has some limitations. First, the major limitation is small sample size and relatively short follow-up period time that for con rmation of results, very larger number of patients and longer follow-up time is needed. Second, for more accurate decision, it was better to compare PRRT with other therapeutic methods such as chemotherapy and somatostatin analogues therapy, but it was not possible in this study. Third, beside to evaluation of treatment response with imaging modalities, it was better measure chromogranin A (CgA) as a NETs marker.

Conclusion
It can be concluded that, since PRRT with 177Lu-DOTATATE in NETs has favorable response rate, few adverse effects and leads to improvement in QOL, it can be used as an effective therapeutic option specially in nonoperative, metastatic and progressive NETs. NET: neuroendocrine tumor; PRRT: peptide receptor radionuclide therapy; RECIST: response evaluation criteria in solid tumors; CR: complete response; PR: partial response; SD: stable disease; PD: progression disease; ECOG: Eastern Cooperative Oncology Group; OS: overall survival; QOL: quality of life; DOTATATE: DOTA0-Tyr3-octreotate; KS: Krenning score; GI: gastrointestinal; LN: lymph node; GBq: gigabecquerel; CTCAE: National Cancer Institute Common Terminology Criteria for Adverse Events.

Declarations
Authors' contributions MZ, INP, MRR, SJR: study design and data collection, SHZ: writing and data collection, EJ: writing, data collection and statistical analysis , ALA: data collection, HD: data collection, MMP: data collection, NJ: writing, MA: writing, statistical analysis, study design and data collection. All authors read and approved the manuscript.

Acknowledgments
This study was granted by Bushehr University of Medical Sciences (no. 302). We thank colleagues at our different units /departments for helping in data collection.

Funding
None.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The study protocol was explained to patients and written consent was obtained from them.