Extended peptide receptor radionuclide therapy: evaluating nephrotoxicity and therapeutic effectiveness in neuroendocrine tumor patients receiving more than four treatment cycles

PURPOSE

Currently, the most used peptide receptor radionuclide therapy (PRRT) regimen for neuroendocrine tumors comprises 4 treatment cycles, and there is not enough large-scale data to support the safety of more individualized extended PRRT. This study aims to evaluate the therapeutic effectiveness and potential nephrotoxicity related to PRRT using more than four treatment cycles.

METHODS

In this retrospective analysis, we included patients who had received at least four PRRT cycles and had available follow-up data. We analyzed renal function indicators before and after multiple treatments, comparing nephrotoxicity in patients receiving four cycles ("standard") with those receiving more than four ("extended treatment"). Nephrotoxicity was assessed via creatinine levels and CTCAE creatinine grades. Treatment effectiveness was gauged using Kaplan-Meier survival analysis, focusing on overall survival and disease-specific survival (DSS). Statistical analyses were performed using SPSS version 26 (IBM), R 4.2.3, and GraphPad Prism 9.0.0. Statistical significance was defined as a P-value of less than 0.05.

RESULTS

Our study cohort consisted of 281 patients in the standard group and 356 in the extended treatment group. No significant differences in baseline characteristics or renal function were noted between the two groups pre-treatment. Mean post-treatment creatinine levels did not significantly differ between the standard (89.30 ± 51.19 μmol/L) and extended treatment groups (93.20 ± 55.98 μmol/L; P = 0.364). Similarly, there was no statistical significance between the CTCAE creatinine grades of the two groups (P = 0.448). Adverse renal events were observed in 0.4% of patients in the standard group and 1.1% in the extended treatment group. After a median follow-up time of 88.3 months, we found that median overall survival was significantly higher in the extended treatment group (72.8 months) compared to the standard treatment group (52.8 months). A Cox regression analysis further supported these findings, indicating a better prognosis for the extended treatment group in terms of overall survival (HR: 0.580, P < 0.001) and DSS (HR: 0.599, P < 0.001).

CONCLUSION

Our findings suggest that extending PRRT treatment beyond the standard four cycles may be a safe and effective therapeutic strategy for NET patients. This approach could be particularly beneficial for patients experiencing disease recurrence or progression following standard treatment.

Complete loss of E-cadherin expression in a rare case of metastatic malignant meningioma: a case report

BACKGROUND

Hematogenous tumor spread of malignant meningiomas occurs very rarely but is associated with very poor prognosis.

CASE PRESENTATION

We report an unusual case of a patient with a malignant meningioma who developed multiple metastases in bones, lungs and liver after initial complete resection of the primary tumor. After partial hepatic resection, specimens were histologically analyzed, and a complete loss of E-cadherin adhesion molecules was found. No oncogenic target mutations were found. The patient received a combination of conventional radiotherapy and peptide receptor radionuclide therapy (PRRT). Due to aggressive tumor behavior and rapid spread of metastases, the patient deceased after initiation of treatment.

CONCLUSIONS

E-cadherin downregulation is associated with a higher probability of tumor invasion and distant metastasis formation in malignant meningioma. Up to now, the efficacy of systemic therapy, including PRRT, is very limited in malignant meningioma patients.

Outcome analysis in patients with metastatic gastroenteropancreatic neuroendocrine tumors receiving peptide receptor radionuclide therapy with Lu-177-DOTATATE

Background

Patients with neuroendocrine tumors (NET) of the gastroenteropancreatic tract (GEP-NET) were effectively treated with peptide receptor radionuclide therapy (PRRT) with Lu-177-DOTATATE in the NETTER-1 trial. The aim of this study was to assess the outcome of metastatic GEP-NET patients within a European Neuroendocrine Tumor Society (ENETS) certified center of excellence after this treatment.

Methods

A total of 41 GEP-NET patients who received PRRT with Lu-177-DOTATATE between 2012 and 2017 at a single center were included in this analysis. Data on pre- and post-PRRT treatments [selective internal radiation therapy (SIRT), somatostatin analogue therapy (SSA), blood parameters, patient symptomatic burden and overall survival] was extracted from patient records.

Results

Overall, PRRT was well tolerated and did not increase patient symptomatic burden. Blood parameters were not significantly affected by PRRT (means before and after therapy: hemoglobin: 125.4 vs. 122.3 mg/L, P=0.201; creatinine: 73.8 vs. 77.7 µmol/L, P=0.146), while leukocytes (6.6 vs. 5.6 G/L, P<0.01) and platelets (269.9 vs. 216.7 G/L, P<0.001) were significantly decreased yet without clinical significance in our study. Seven of 9 patients with SIRT treatment prior to PRRT were deceased (mortality odds ratio =4.083). The mortality odds ratio of patients with a pancreatic tumor and SIRT was 1.33 compared to patients with a different tumor origin. 6 of 15 patients (40%) with post-PRRT SSA were deceased (mortality odds ratio =0.429 without SSA after PRRT).

Conclusions

Patients with advanced GEP-NET might benefit from PRRT with Lu-177-DOTATATE as it can provide a valuable treatment modality in advanced disease stages. Safety profiles of PRRT were manageable without increasing the symptomatic burden. SIRT before PRRT or lack of SSA after PRRT seem to impair the response and reduce survival.

Role of systemic inflammatory factors in gastroenteropancreatic neuroendocrine tumors (GEP-NETs) treated with peptide receptor radionuclide therapy (PRRT): From biology to theragnosis

AIM

Systemic inflammatory factors have been validated as indicators of ongoing systemic inflammation that could be predictive markers of poor prognosis for oncological outcomes. However, the prognostic impact of systemic inflammation markers is unknown in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs) treated with peptide receptor radionuclide therapy (PRRT).

METHODS

We conducted an observational, retrospective, multicentric study of 40 patients with GEP or unknown origin NETs treated with PRRT between 2016 and 2020. The systemic inflammatory markers were calculated as follows: neutrophil to lymphocyte ratio (NLR)=neutrophil count/lymphocyte count, monocyte to lymphocyte ratio (MLR)=monocyte count/lymphocyte count, platelet to lymphocyte ratio (PLR)=platelet count/lymphocyte count, albumin to lymphocyte ratio (ALR)=albumin levels/lymphocyte count and derived Neutrophil to Lymphocyte ratio (dNLR)=neutrophil count/(leucocytes count - neutrophils count). Baseline analysis and after the second dose were used for the calculation of different ratios.

RESULTS

The median age was 63 years (range 41-85), 55% were male. The baseline cut-off values for NLR were 2.61, for MLR 0.31, for PLR 110.14, for ALR 2.39 and for dNLR 1.71. The cut-off values after the 2° dose were, for NLR 2.3, for MLR 0.3, for PLR 131.61, ALR 4.16, and dNLR 1.48. Median progression-free survival (PFS) was 21.7 months (95% CI 10.7-32.8 months) and overall survival (OS) was 32.1 months (95% CI 19.6-44.7 months), PFS was shorter in patients with elevated NLR (p=0.001), ALR (0.03), and dNLR (p=0.001) in baseline analysis. DCR was 81% and ORR 18%.

CONCLUSIONS

In GEP or unknown origin NETs treated with PRRT, we have identified the predictive and prognostic impact of baseline systemic inflammatory factors.

Light It Up! The Use of DOTATATE in Diagnosis and Treatment of Neuroendocrine Neoplasms

Radiolabeled somatostatin analogs are increasingly used in the diagnosis and treatment of neuroendocrine tumors. Diagnostic imaging with 68Ga-DOTATATE PET/CT has demonstrated the improved sensitivity in detecting primary and metastatic neuroendocrine lesions compared with conventional imaging and prior generation somatostatin receptor imaging. Peptide receptor radionuclide therapy with 177Lu-DOTATATE is now frequently included in the management of neuroendocrine neoplasms, with prospective randomized control studies demonstrating its beneficial impact on survival and quality of life. Nonetheless, peptide rector radionuclide therapy is still considered palliative rather than curative and may be accompanied by adverse effects.

Feasibility and therapeutic potential of the 68Ga/177Lu-DOTATATE theranostic pair in patients with metastatic medullary thyroid carcinoma

BACKGROUND

This study assessed: 1) the clinical efficacy of imaging with 68Ga-DOTATATE PET/CT (SSTR (somatostatin receptor)-PET) to detect medullary thyroid carcinoma (MTC); and 2) the therapeutic efficacy of peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE in MTC patients.

MATERIALS AND METHODS

Patients with histologically proven MTC and suspected recurrence following thyroidectomy, based on raised serum calcitonin levels, underwent SSTR-PET. In addition, to evaluate the clinical efficacy and safety of PRRT, the patients with intense uptake on SSTR-PET or 99mTc-octreotide scintigraphy underwent PRRT. The Common Terminology Criteria for Adverse Events (version 4.03) was used to grade adverse events after PRRT. Treatment response was classified as complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD).

RESULTS

Twenty MTC patients (10 male, 10 female) with a median age of 48.5 years underwent SSTR-PET. SSTR-PET was positive in 17/20 patients (85%). Four of the 17 patients with positive SSTR-PET were scheduled for PRRT. In addition, 2 patients had positive 99mTc-octreotide scintigraphy results (Krenning score ≥ 2) and were scheduled for PRRT. Two of the 6 patients who underwent PRRT showed PR, 2 SD and 2 PD. Two patients died during the follow-up period. Median overall survival was 19 months (95% CI: 5.52-29.48). There were no cases of significant toxicity.

CONCLUSION

Radiolabeled somatostatin analogs are contributive for the management of recurrent MTC. 68Ga-DOTATAE PET-CT showed a relatively high detection rate in recurrent MTC. In addition, PRRT with 177Lu-DOTATATE was found to be a safe alternative therapeutic option for MTC.

Peptide Receptor Radionuclide Therapy: Looking Back, Looking Forward

Peptide receptor radionuclide therapy (PRRT) is a highly effective anti-cancer treatment modality for patients with non-resectable, metastasized neuroendocrine tumors (NETs). During PRRT, specific receptors that are overexpressed on the cancer cells are targeted with a peptide labeled with a DNA-damaging radionuclide. Even though PRRT is a powerful treatment for metastasized NET patients, the majority still cannot be cured at this stage of the disease. Hence, many investigators focus on improving the therapeutic efficacy of this therapy. Improving PRRT can, for example, be achieved by using other radionuclides with different physical properties, by combining PRRT with radiosensitizing agents or by radiolabeling peptides with different characteristics. However, due to lack of extensive knowledge of radiobiological responses of cancer cells to PRRT, biological parameters that influence absorbed dose or that might even elicit insensitivity to therapy remain elusive and the context in which these improvements will be successful warrants further investigation. In this review, we will discuss the development of PRRT, its clinical merits in current treatment and future perspectives. We will highlight different radionuclides and their benefits and pitfalls, as well as different peptide-conjugates that hold these radionuclides. We will zoom in on the latest developments regarding combinatorial treatments and how investigators from different disciplines such as dosimetry and radiobiology are now joining forces to improve PRRT for NETs.

Differences in the expression of SSTR1-5 in meningiomas and its therapeutic potential

Beyond microsurgical resection and radiation therapy, there are currently no established treatment alternatives for meningioma patients. In selected cases, peptide radio receptor therapy (PRRT) can be implemented. For this purpose, a radionuclide is bound to a substance targeting specific receptors in meningiomas. One of them is somatostatin receptor 2, which can be found in most meningiomas. However, other somatostatin receptors (SSTR) exist, but their expressions have only been described in small case series. In this study, we analyzed the expression of SSTR1, 2A, 3, 4, and 5 in a large cohort of meningiomas in order to enable further refinement of this innovative treatment option. Overall, 726 tumor samples were processed into tissue microarrays and stained for SSTR1, 2A, 3, 4, and 5 immunohistochemically. Microscopic evaluation was done with an established semiquantitative score regarding percentual quantification and staining intensity, and results were correlated with clinical data. There was a significant lower rate of SSTR1 expression in meningiomas of male patients. Older age was associated with higher expression of SSTR1, 2A, and 5 and lower scores for SSTR3 and 4. Tumors treated with radiotherapy before resection showed lower rates of SSTR1 and 5 expression, while recurrent meningiomas had lower SSTR1 scores. Tumor tissue from patients suffering from neurofibromatosis type 2 had lower expression scores for SSTR1, 2, and 5. For SSTR3 and 4, NF2 patients showed higher scores than sporadic tumors. Spinal meningiomas had higher scores for SSTR1, 4, and 5 compared tumor location of the skull base and convexity/falx. Overall, higher WHO grade was associated with lower SSTR scores. While all SSTRs were expressed, there are marked differences of SSTR expression between meningioma subgroups. This has the potential to drive the development of more selective PRRT substances with higher treatment efficacy.

First-in-human study of novel SSTR antagonist 177Lu-DOTA-LM3 for peptide receptor radionuclide therapy in patients with metastatic neuroendocrine neoplasms: dosimetry, safety and efficacy

The objective of this study was to assess the safety, dosimetry, and efficacy of the ¹⁷⁷Lu-labeled somatostatin receptor (SSTR) antagonist DOTA-p-Cl-Phe-cyclo (D-Cys-Tyr-D-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)D-Tyr-NH2 (¹⁷⁷Lu-DOTA-LM3) in patients with metastatic neuroendocrine neoplasms (NENs). Methods: Fifty-one patients (age 27-76, mean 51.6±13.9 years) with metastatic NENs underwent peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTA-LM3 between August 2017 and December 2019. The median administered activity per cycle was 6.1±0.88 GBq (range 2.8-7.4 GBq). ⁶⁸Ga-NODAGA-LM3 PET/CT was used for patient selection and follow-up after ¹⁷⁷Lu-DOTA-LM3 PRRT. Morphologic and molecular responses were evaluated in accordance with RECIST 1.1 and European Organization for Research and Treatment of Cancer (EORTC) criteria. Treatment-related adverse events were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 5.0. Dosimetry was performed in 11 patients and compared with the SSTR agonist ¹⁷⁷Lu-DOTATOC in 247 patients undergoing PRRT on the same dosimetry protocol. Results: Higher uptake and a longer effective half-life of ¹⁷⁷Lu-DOTA-LM3 was found for whole-body as well as kidneys, spleen, and metastases, resulting in higher mean absorbed organ and tumor doses as compared to the agonist ¹⁷⁷Lu-DOTA-TOC. All patients tolerated therapy without any serious acute adverse effects. Mild nausea without vomiting was observed in 5 (9.8%) patients; no other symptoms were reported. The most severe delayed adverse event was CTC-3 thrombocytopenia in 3 (5.9%) patients. Neither CTC-4 thrombocytopenia nor CTC-3-4 anemia or leukopenia was observed after treatment. No significant decline in renal function was observed, nor was hepatotoxicity. According to RECIST 1.1, disease control could be reached in 40 patients (disease control rate, 85.1%) of 47 patients monitored after ¹⁷⁷Lu-DOTA-LM3 PRRT, with a partial response in 17 (36.2%) and stable disease in 23 (48.9%), whereas 7 (14.9%) patients had progressive disease, and by EORTC criteria, complete remission in 2 (4.3%), partial remission in 21 (44.7%), stable disease in 18 (38.3%), and progressive disease in 6 (12.8%) patients. Conclusion: "Antagonist PRRT" with ¹⁷⁷Lu-DOTA-LM3 could be administered without severe adverse effects and was well tolerated by the majority of patients, with thrombocytopenia occurring only in a few patients. No other severe adverse effects were observed, particularly no nephrotoxicity. The SSTR antagonist ¹⁷⁷Lu-DOTA-LM3 appears to be very promising for PRRT, provides favorable biodistribution and higher tumor radiation doses than SSTR agonists, and was very effective in treating advanced metastatic NENs, especially in patients with low or no SSTR agonist binding, even achieving complete remission in some patients.

Surgical feasibility, Determinants and overall Efficacy assessment of Neoadjuvant PRRT with 177Lu-DOTATATE for Locally Advanced Unresectable Gastroenteropancreatic Neuroendocrine Tumors

OBJECTIVE: The aim of the study was to assess ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) in neoadjuvant setting in gastroenteropancreatic neuroendocrine tumors (GEP-NETs). In addition, we also evaluated the variables associated with resectability of the primary following PRRT. MATERIALS AND METHODS: A total of 57 GEP-NETs with unresectable primary due to vascular involvement as defined using the National Comprehensive Cancer Network (NCCN) criteria given for pancreatic ductal adenocarcinoma (PDAC), who underwent ¹⁷⁷Lu-DOTATATE without any prior surgery were included in this study. GEP-NETs were divided into two groups: Group1-without liver metastases (n = 23 patients) and Group2- with potentially resectable liver metastases (n = 34 patients). ¹⁷⁷Lu-DOTATATE was administered with mixed amino acid-based renal protection with dose of 7.4 GBq (200 mCi) per cycle. Evaluation of surgical resectability following PRRT was done by using tri-phasic computed tomography (CT) imaging. Overall PRRT response was evaluated under four broad categories. The Kaplan-Meier product-limit method was used to calculate progression free survival (PFS) and overall survival (OS). Associations between variables and resectable primary after PRRT were analyzed by using Chi-square test at significant P value less than 0.05. RESULTS: Following ¹⁷⁷Lu-DOTATATE, unresectable primary became resectable in 15 out of 57 (26.3%) patients {7 patients in group-1 and 8 patients in group-2}. Response (complete response and partial response) to PRRT was seen in 48 patients (84%), 23 patients (40%), 18 patients (31%) and 23 patients (40%) on symptomatic, biochemical, molecular imaging and anatomical imaging response evaluation criteria respectively. Estimated rates of PFS were 95% and 90% at 2 years in group1 and group2 patients respectively. The 2-years OS of combined both groups was 92.1%. Higher rate of resectable primary following PRRT was found in duodenal NET, GEP-NETs with absent regional lymph node involvement, size of primary<5cm, size of liver lesions ≤1.5 cm, number of liver lesions ≤3 and FDG uptake(SUV_max<5 in primary tumor) with significant P value. CONCLUSION: Thus, unresectable primary converted could be into resectable in a moderate fraction of GEP-NETs following ¹⁷⁷Lu-DOTATATE, signifying that neoadjuvant PRRT could be considered in GEP-NETs patients with unresectable primary due to vascular involvement with or without liver metastases. Effective control of symptoms with favorable morphological and functional imaging response and durable PFS and OS following ¹⁷⁷Lu-DOTATATE PRRT were important observation in our study, which may lead to less morbidity and mortality in these patients.

Therapy-related myeloid neoplasm after peptide receptor radionuclide therapy (PRRT) in 1631 patients from our 20 years of experiences: prognostic parameters and overall survival

PURPOSE

To determine prognostic factors and overall survival (OS) in therapy-related myeloid neoplasm (t-MN) of patients after receiving peptide receptor radionuclide therapy (PRRT).

METHODS

All patients treated from February 1999 until September 2019 at our center who had bone marrow biopsy-proven t-MN after PRRT were included. Patient characteristics, laboratory results, and all tumor-directed therapies before t-MN diagnosis were collected. Cox regression analysis was performed to identify parameters associated with OS. Receiver operating characteristic (ROC) curve analysis was used to define cutoff values as well as sensitivity and specificity of the parameters.

RESULTS

Out of 1631 patients treated with PRRT, 30 patients developed t-MN comprising myelodysplastic syndrome (MDS) in 23 patients (77%) and acute myeloid leukemia (AML) in 7 patients (23%). The median OS of t-MN patients was 13 months (range 9.1-16.9 months): 6 months for AML and 15 months for the MDS subgroup, respectively. Higher platelet level was a significant prognostic parameter for longer OS (hazard ratio (HR): 0.99, P < 0.05). Using ROC analysis, the best cutoff value for thrombocyte count was 183.5 Gpt/L, resulting in a sensitivity of 92.3% and a specificity of 50%. Other factors, such as hemoglobin level, did not show a significant correlation with OS.

CONCLUSION

Even rarely occurred, the OS is gravely compromised in t-MN patients after PRRT, and even less in the AML subgroup (6 months). Higher platelet value was a significant prognostic parameter for longer OS in t-MN patients.

Does the proteasome inhibitor bortezomib sensitize to DNA-damaging therapy in gastroenteropancreatic neuroendocrine neoplasms? - A preclinical assessment in vitro and in vivo

BACKGROUND

Well-differentiated gastroenteropancreatic neuroendocrine neoplasms are rare tumors with a slow proliferation. They are virtually resistant to many DNA-damaging therapeutic approaches, such as chemo- and external beam therapy, which might be overcome by DNA damage inhibition induced by proteasome inhibitors such as bortezomib.

METHODS AND RESULTS

In this study, we assessed several combined treatment modalities in vitro and in vivo. By cell-based functional analyses, in a 3D in ovo and an orthotopic mouse model, we demonstrated sensitizing effects of bortezomib combined with cisplatin, radiation and peptide receptor radionuclide therapy (PRRT). By gene expression profiling and western blot, we explored the underlying mechanisms, which resulted in an impaired DNA damage repair. Therapy-induced DNA damage triggered extrinsic proapoptotic signaling as well as the induction of cell cycle arrest, leading to a decreased vital tumor volume and altered tissue composition shown by magnetic resonance imaging and F-18-FDG-PET in vivo, however with no significant additional benefit related to PRRT alone.

CONCLUSIONS

We demonstrated that bortezomib has short-term sensitizing effects when combined with DNA damaging therapy by interfering with DNA repair in vitro and in ovo. Nevertheless, due to high tumor heterogeneity after PRRT in long-term observations, we were not able to prove a therapeutic advantage of bortezomib-combined PRRT in an in vivo mouse model.

131I-MIBG negative progressive symptomatic metastatic paraganglioma: response and outcome with 177Lu-DOTATATE peptide receptor radionuclide therapy

OBJECTIVE

The primary aim of this study was to evaluate the long-term outcome of ¹⁷⁷Lu-DOTATATE PRRT in terms of clinical, biochemical and imaging response rates, disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) in ¹³¹I-metaiodobenzylguanidine (MIBG) negative progressive/symptomatic locally advanced or metastatic paragangliomas (PGL). The secondary aims of this study were to determine clinical toxicity of ¹⁷⁷Lu-DOTATATE and association of PFS with various variables.

MATERIALS AND METHODS

¹³¹I-MIBG negative PGL with progressive/symptomatic locally advanced or metastatic disease that underwent ¹⁷⁷Lu-DOTATATE PRRT from 2012 to 2019 in our institute were evaluated. Standard dose activity of 5.55-7.4 GBq per cycle of ¹⁷⁷Lu-DOTATATE was administered in somatostatin receptor (SSTR) positive PGL. Post-PRRT response was evaluated under three broad categories: (a) symptomatic, (b) biochemical, and (c) imaging (molecular and anatomic imaging). The PFS and OS since first ¹⁷⁷Lu-DOTATATE cycle were determined. Associations of PFS with various variables were also investigated. The clinical toxicities of ¹⁷⁷Lu-DOTATATE in PGL were determined.

RESULTS

Amongst a total of 9 PGL patients, response to ¹⁷⁷Lu-DOTATATE was seen in six patients, two patients, four patients and three patients on symptomatic, biochemical, molecular and anatomical based imaging response evaluation categories respectively with DCR of 67%. The median PFS and OS were not reached at a median follow-up of 40 months. Estimated PFS rate of 63% (95% CI 30-96%) and OS rate of 65% (95% CI 32-97%) were noticed at 40 months. Significant association of PFS was found for site of PGL (non-HNPGL), total cumulative dose of PRRT (> 22.2 GBq), and number of PRRT cycles patient received (≥ 4cycles). ¹⁷⁷Lu-DOTATATE was well tolerated without acute catecholamine crisis, nephrotoxicity or bone marrow suppression of any grade or high-grade (grade ≥ 2) hematological toxicities.

CONCLUSION

Our study showed favorable results with minimal low-grade and easily manageable side effects of ¹⁷⁷Lu-DOTATATE in patients of PGL. Thus, ¹⁷⁷Lu-DOTATATE may be considered as promising therapeutic option in ¹³¹I-MIBG negative and SSTR positive subset of PGL cases. However, further prospective study in a large number of patients is required for validation of our study results.

Long-term outcome of "Sandwich" chemo-PRRT: a novel treatment strategy for metastatic neuroendocrine tumors with both FDG- and SSTR-avid aggressive disease

OBJECTIVE

The primary aims of this study were to evaluate the long-term outcome of a "sandwich chemo-PRRT (SCPRRT)" regimen with regard to therapeutic response rate, progression-free survival (PFS), and overall survival (OS) rates in metastatic neuroendocrine tumors (NETs) with both somatostatin receptor (SSTR)- and fluorodeoxyglucose (FDG)-avid aggressive disease. Additionally, health-related quality of life (HRQoL) scales, clinical toxicity, and association of PFS and disease control rate (DCR) with various variables were also evaluated.

MATERIALS AND METHODS

A total of 38 patients of the aforementioned cohort, who received SCPRRT (at least 2 cycles of each PRRT and chemotherapy) at our institute between January 2012 and December 2018, were included and analyzed in this retrospective study. Between two cycles of ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT), two cycles of oral capecitabine and temozolomide (CAPTEM) were sandwiched. Therapeutic responses following SCPRRT were assessed by using pre-defined criteria. PFS and OS after first SCPRRT were determined. Eastern Cooperative Oncology Group (ECOG) and Karnofsky score were used for evaluation of HRQoL before and after SCPPRT in all 38 patients. Any adverse events were graded according to the Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0) of the National Cancer Institute. Associations of PFS and DCR with various variables were evaluated.

RESULTS

Response (complete response and partial response) to SCPRRT was seen in 28 patients (73%), 15 patients (39%), and 16 patients (42%) on symptomatic, biochemical, and molecular imaging response evaluation criteria respectively. A total of 17 patients (45%) had anatomical imaging response with DCR of 84% based upon the RECIST 1.1 criteria. Pre-therapy mean ECOG and KPS was 2.0 and 68, which changed to 1.0 and 75 respectively following SCPRRT. Long-term follow-up data was available and ranged from 12 to 65 months after the first SCPRRT. Median PFS and OS were not reached at a median follow-up of 36 months. An estimated PFS rate of 72.5% and OS rate of 80.4% was found at 36 months. Longer PFS was dependent upon high SSTR uptake and number of CAPTEM cycle (≥ 7 cycles), absence of skeletal metastasis, and no previous external beam radiotherapy (EBRT) exposure with significant P value. Higher DCR was dependent upon absence of skeletal metastasis with significant P value. SCPRRT was tolerated well with none developing grade 4 hematotoxicity and nephrotoxicity of any grade. Anemia (grade 3), thrombocytopenia (grade 3), and leukopenia (grade 3) were noticed in 1 patient (2.5%), 2 patients (5%), and 1 patient (2.5%) respectively in this study.

CONCLUSION

Thus, favorable response rates with effective control of symptoms and longer PFS and OS without high-grade or life-threatening toxicities were important observations in the present study following SCPRRT in NET patients with aggressive, both FDG- and SSTR-avid, metastatic progressive disease. The study results indicate the potential role of "sandwich chemo-PRRT" in future therapeutic algorithms of aggressive, both SSTR- and FDG-positive subset of neuroendocrine tumors.

Patient Selection and Toxicities of PRRT for Metastatic Neuroendocrine Tumors and Research Opportunities

OPINION STATEMENT

Neuroendocrine tumors (NETs) are a heterogenous group of neoplasms characterized by varied biological hallmarks and behavior, ranging from indolent to aggressive. For many decades, somatostatin analogues and few targeted therapies were available for NETs and these therapies had minimal response rates. However, there have been a number of recent treatment advances. Peptide receptor radionuclide therapy (PRRT) is a novel approach to treatment of NETs and has changed the landscape of treatment for NETs. It is a form of targeted therapy in which a radiolabeled somatostatin analogue delivers radiation specifically to tumor cells expressing the somatostatin receptor.

Dosimetry after peptide receptor radionuclide therapy: impact of reduced number of post-treatment studies on absorbed dose calculation and on patient management

Background

After each cycle of [¹⁷⁷Lu]-DOTA-TATE peptide receptor radionuclide therapy (PRRT) dosimetry is performed to enable precise calculation of the radiation-absorbed dose to tumors and normal organs. Absorbed doses are routinely calculated from three quantitative single-photon emission computed tomography (SPECT) studies corrected by computed tomography (CT) acquired at t₁ = 24 h, t₂ = 96 h, and t₃ = 168 h after the first cycle of treatment. After following cycles, a single SPECT/CT study is performed. The aim of the present study is to assess the feasibility of a “two time point” quantitative SPECT/CT protocol after the first PRRT cycle and its impact on patient management.

Quantitative SPECT/CT data of 25 consecutive patients with metastatic neuroendocrine tumors after PRRT were retrospectively analyzed. Radiation-absorbed doses calculated using the standard protocol with three SPECT/CT studies acquired at (t₁, t₂, t₃) were compared to those obtained from three different “two time point” protocols with SPECT/CT studies performed at (t₁, t₂), (t₁, t₃), or (t₂, t₃).

Results

The best agreement for the cumulative doses absorbed by the kidneys, bone marrow, liver, spleen, and tumors with the conventional protocol was obtained with the (t₁, t₃) protocol with mean relative differences of − 1.0% ± 2.4%, 0.4% ± 3.1%, − 0.9% ± 4.0%, − 0.8% ± 1.1%, and − 0.5% ± 2.0%, respectively, and correlation coefficients of r = 0.99 for all.

In all patients, there was no difference in the management decision of whether or not to stop PRRT because of unsafe absorbed dose to risk organs using either the standard protocol or the (t₁, t₃) protocol.

Conclusion

These preliminary results demonstrate that dosimetry calculations using two quantitative SPECT/CT studies acquired at 24 and 168 h after the first PRRT cycle are feasible and are in good agreement with the standard imaging protocol with no change in patient management decisions, while enabling improved patient comfort and reduced scanner and staff time.

Dose escalation of an Evans blue-modified radiolabeled somatostatin analog 177Lu-DOTA-EB-TATE in the treatment of metastatic neuroendocrine tumors

PURPOSE

To evaluate the safety and efficacy of ¹⁷⁷Lu-DOTA-EB-TATE, a radiolabeled somatostatin analog modified by Evans blue, at escalating doses, was used to increase tumor retention in patients with progressive metastatic neuroendocrine tumors (NETs).

METHODS

Thirty-three patients with metastatic NETs were prospectively enrolled into four groups: group A (n = 6, 43 ± 12 years) administered approximately 3.7 GBq (100 mCi) ¹⁷⁷Lu-DOTATATE as controls; group B (n = 7, 55 ± 7 years) administered approximately 1.11 GBq (30 mCi) ¹⁷⁷Lu-DOTA-EB-TATE; group C (n = 6, 55 ± 10 years) administered approximately 1.85 GBq (50 mCi) ¹⁷⁷Lu-DOTA-EB-TATE; group D (n = 14, 50 ± 10 years) administered approximately 3.7 GBq (100 mCi) ¹⁷⁷Lu-DOTA-EB-TATE. Treatment-related adverse events were graded according to the CTCAE v.5.0. ⁶⁸Ga-DOTATATE PET/CT were performed at baseline and 2-3 months after treatment for response evaluation.

RESULTS

Administration was well tolerated. No CTC 3/4 hematotoxicity, nephrotoxicity, or hepatotoxicity was observed during or after treatment in groups A-C. In group D, CTC-3 hematotoxicity was recorded in 2 patients with multicourse chemotherapy previously. After one-cycle treatment, the SUVmax decreased in group C (Δ% = - 17.4 ± 29.3%) and group D (Δ% = - 15.1 ± 39.1%), but greatly increased in group B (Δ% = 30.0 ± 68.0%) and mildly increased in group A (Δ% = 5.4 ± 45.9%). Referring to EORTC criteria, 16.7% (1/6), 0% (0/7), 50% (3/6), and 50% (7/14) were evaluated as partial response in groups A, B, C, and D, respectively. When selecting lesions with comparable baseline SUVmax ranging from 15 to 40, SUVmax showed no significant decrease in group B (Δ% = - 7.3 ± 24.5%) (P = 0.214), significant decrease in group C (Δ% = - 34.9 ± 12.4%) (P = 0.001), and in group D (Δ% = - 17.9 ± 19.7%) (P = 0.012) as compared with group A with increased SUVmax (Δ% = 8.4 ± 48.8%). SUVmax significantly decreased in the EBTATE groups (groups B-D combined) (Δ% = - 19.0 ± 21.5%) as compared with the TATE group (P = 0.045).

CONCLUSION

¹⁷⁷Lu-DOTA-EB-TATE is well tolerated and is more effective than ¹⁷⁷Lu-DOTATATE. Both 1.85 GBq (50 mCi) and 3.7 GBq (100 mCi) doses appear to be more effective than 1.11 GBq (30 mCi) dose. Further investigation with more cycles of ¹⁷⁷Lu-DOTA-EB-TATE treatment and longer follow-up is warranted.

TRIAL REGISTRATION

Treatment Using 177Lu-DOTA-EB-TATE in Patients with Advanced Neuroendocrine Tumors (NCT03478358). URL: https://register.clinicaltrials.gov/prs/app/action/ViewOrUnrelease?uid=U0001JRW&ts=13&sid=S0007RNX&cx=y3yqv4.

Prolonged response to 177Lu-DOTATATE therapy of a bone marrow infiltration in a refractory thymic neuro endocrine tumor

Thymic neuro endocrine tumor (tNET) are extremely rare malignancies with poor prognosis, requiring investigation of novel therapeutic approaches. ¹⁷⁷Lu-DOTATATE is a successful systemic treatment modality in patients with metastatic gastroenteropancreatic but it role in tNET is not yet well established. Here we report a case of a 39-year-old man with refractory bone marrow infiltration of a tNET, treated by 4 cycles of peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu DOTATATE. Since the first cycle, clinical symptoms were substantially decreased, without any severe subacute haematological toxicity. Three months after the end of PRRT, both ⁶⁸Ga-DOTATOC and ¹⁸F-FDG PET confirmed a partial response, already suggested by ¹⁷⁷Lu-DOTATATE treatment scan with a significant decrease of the bone marrow uptake between the first and fourth cycle. This report highlights that PRRT could be an effective therapeutic option for advanced bone metastatic disease tNET, with the significant benefit of alleviation of bone pain and radiologic response, without severe or irreversible haematotoxicity.

Molecular Imaging and Therapy for Neuroendocrine Tumors

OPINION STATEMENT

Neuroendocrine tumors (NETs) are relatively rare, with 12,000-15,000 new cases diagnosed annually in the USA. Although NETs are a diverse group of neoplasms, they share common molecular targets that can be exploited using nuclear medicine techniques for both imaging and therapy. NETs have traditionally been imaged with SPECT imaging using ¹¹¹In-labeled octreotide analogs to detect neoplasms with somatostatin receptors. In addition, certain NETs (pheochromocytomas, paragangliomas, and neuroblastomas) are also effectively imaged using ¹²³I- or ¹³¹I-labeled metaiodobenzylguanidine (MIBG), an analog of guanethidine. More recently, PET imaging with ⁶⁸Ga-labeled somatostatin receptor (SSR) analogs allows neuroendocrine tumors to be imaged with much higher sensitivity. ⁶⁸Ga-DOTATATE was approved as a PET tracer by the FDA in June 2016. In addition to imaging, both MIBG and DOTATATE can be labeled with therapeutic radionuclides to deliver targeted radiation selectively to macroscopic and microscopic tumor sites. The incorporation of the same molecular probe for imaging and therapy provides a radio-theranostic approach to identifying, targeting, and treating tumors. Over the years, several centers have experience treating NETs with high-dose ¹³¹I-MIBG. ¹⁷⁷Lu-DOTATATE was approved by the FDA in 2018 for treatment of gastroenteropancreatic NETs and constitutes a major advancement in the treatment of these diseases. In this paper, we provide an overview of imaging and treating neuroendocrine tumors using MIBG and SSR probes. Although uncommon, neuroendocrine tumors have provided the largest experience for targeted radionuclide imaging and therapy (with the exception of radioiodine treatment for thyroid disease). In addition to benefitting patients with these rare tumors, the knowledge gained provides a blueprint for the development of future paired diagnostic/therapeutic probes for treating other diseases, such as prostate cancer.

Predictive power of the post-treatment scans after the initial or first two courses of [177Lu]-DOTA-TATE

BACKGROUND

The aim of this study was to evaluate the predictive power of the absorbed dose to kidneys after the first course of treatment with [¹⁷⁷Lu]-DOTA-TATE for neuroendocrine tumors (NETs) on the cumulative kidney absorbed dose after 3 or 4 cycles of treatment. Post-treatment scans (PTS) are acquired after each cycle of peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE for personalized radiation dosimetry in order to ensure a cumulative absorbed dose to kidneys under a safety threshold of 25 Gy. One hundred eighty-seven patients who completed treatment with [¹⁷⁷Lu]-DOTA-TATE and underwent PTS for dosimetry calculation were included in this retrospective study. The correlation between the cumulative absorbed dose to kidneys after the completion of treatment and the absorbed dose after the first cycle(s) was studied. Multilinear regression analysis was done to predict the cumulative absorbed dose to the kidneys of the subsequent cycles, and an algorithm for the follow up of kidney absorbed dose is proposed.

RESULTS

Patients whose absorbed dose to kidneys after the first cycle of treatment is below 5.6 Gy can receive four cycles of treatment with a cumulative dose less than 25 Gy (p < 0.1). For the other patients, the cumulative absorbed dose after 3 or 4 cycles of treatment can be predicted after the second cycle of treatment to allow for an early decision regarding the number of cycles that may be given.

CONCLUSIONS

The follow up of kidney absorbed dose after PRRT can be simplified with the algorithm presented in this study, reducing by one-third the number of post-treatment scans and reducing hospitalization time for more than half of the treatment cycles.

Reducing the number of CTs performed to monitor personalized dosimetry during peptide receptor radionuclide therapy (PRRT)

Background

Peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE is an effective treatment of neuroendocrine tumors (NETs). After each cycle of treatment, patient dosimetry evaluates the radiation dose to the risk organs, kidneys, and bone marrow, the most radiosensitive tissues. Absorbed doses are calculated from the radioactivity in the blood and from single photon emission computed tomography (SPECT) images corrected by computed tomography (CT) acquired after each course of treatment. The aim of this work is to assess whether the dosimetry along all treatment cycles can be calculated using a single CT. We hypothesize that the absorbed doses to the risk organs calculated with a single CT will be accurate enough to correctly manage the patients, i.e., whether or not to continue PRRT.

Twenty-four patients diagnosed with metastatic NETs undergoing PRRT with [¹⁷⁷Lu]-DOTA-TATE were retrospectively included in this study. We compared radiation doses to the kidneys and bone marrow using two protocols. In the “classical” one, dosimetry is calculated based on a SPECT and a CT after each treatment cycle. In the new protocol, dosimetry is calculated based on a SPECT study after each cycle but with the first acquired CT for all cycles.

Results

The decision whether or not to stop PRRT because of unsafe absorbed dose to the risk organs would have been the same had the classical or the new protocol been used. The agreement between the cumulative doses to the kidneys and bone marrow obtained from the two protocols was excellent with Pearson’s correlation coefficients r = 0.95 and r = 0.99 (P < 0.0001) and mean relative differences of 5.30 ± 6.20% and 0.48 ± 4.88%, respectively.

Conclusions

Dosimetry calculations for a given patient can be done using a single CT registered to serial SPECTs. This new protocol reduces the need for a hybrid camera in the follow-up of patients receiving [¹⁷⁷Lu]-DOTA-TATE.

Correlation of dose with toxicity and tumour response to 90Y- and 177Lu-PRRT provides the basis for optimization through individualized treatment planning

PURPOSE

Peptide receptor radionuclide therapy (PRRT) with ⁹⁰Y-labelled and ¹⁷⁷Lu-labelled peptides is an effective strategy for the treatment of metastatic/nonresectable neuroendocrine tumours (NETs). Dosimetry provides important information useful for optimizing PRRT with individualized regimens to reduce toxicity and increase tumour responses. However, this strategy is not applied in routine clinical practice, despite the fact that several dosimetric studies have demonstrated significant dose-effect correlations for normal organ toxicity and tumour response that can better guide therapy planning. The present study reviews the key relationships and the radiobiological models available in the literature with the aim of providing evidence that optimization of PRRT is feasible through the implementation of dosimetry.

METHODS

The MEDLINE database was searched combining specific keywords. Original studies published in the English language reporting dose-effect outcomes in patients treated with PRRT were chosen.

RESULTS

Nine of 126 studies were selected from PubMed, and a further five were added manually, reporting on 590 patients. The studies were analysed and are discussed in terms of weak and strong elements of correlations.

CONCLUSION

Several studies provided evidence of clinical benefit from the implementation of dosimetry in PRRT, indicating the potential contribution of this approach to reducing severe toxicity and/or reducing undertreatment that commonly occurs. Prospective trials, possibly multicentre, with larger numbers of patients undergoing quantitative dosimetry and with standardized methodologies should be carried out to definitively provide robust predictive paradigms to establish effective tailored PRRT.

Management of NFAs: medical treatment

INTRODUCTION

Non-functioning pituitary adenomas (NFPAs) are in general large tumors that present with symptoms secondary to local pressure on adjacent structures. Transsphenoidal surgery is the first line of treatment but residual tumor mass is often detected post-operatively. Medical therapy, in any stage of tumor management, is not well established.

METHODS

A literature search was performed to review the available data on medical treatment of NFPAs.

RESULTS

Medications investigated for the treatment of NFPAs include dopamine receptor agonists (DA) and somatostatin receptor ligands. Randomized controlled trials are lacking, but available data suggest that DA have a positive effect on tumor remnant stabilization after surgery and could be considered in this setting. Temozolomide is reserved for aggressive tumors, although future studies are required.

CONCLUSIONS

NFPA are often not amenable to complete surgical resection. Conservative follow-up after surgery is associated with a high prevalence of tumor remnant progression. DA therapy may prevent residual tumor enlargement in over 85% of these patients, with a substantial consequent reduction in the need for repeat surgery or radiation therapy. It is our view that DA treatment should be routinely considered for the management of NFPA patients with incompletely resected tumors.

Peptide Receptor Radionuclide Therapy-Induced Gitelman-like Syndrome

Peptide receptor radionuclide therapy (PRRT) is a molecular-targeted therapy in which a somatostatin analogue (a small peptide) is coupled with a radioligand so that the radiation dose is selectively administered to somatostatin receptor-expressing metastasized neuroendocrine tumors, particularly gastroenteropancreatic. Reported toxicities include myelotoxicity and nephrotoxicity, the latter manifesting as decreased kidney function, often developing months to years after treatment completion. We present a case of PRRT-induced kidney toxicity manifesting as a severe Gitelman-like tubulopathy with preserved kidney function. Because profound hypokalemia and hypocalcemia can lead to life-threatening arrhythmias, we highlight the necessity for careful monitoring of serum and urine electrolytes in patients receiving PRRT.

Physiologically based pharmacokinetic modeling of (18)F-SiFAlin-Asp3-PEG1-TATE in AR42J tumor bearing mice

PURPOSE

Peptide receptor radionuclide therapy (PRRT) is commonly performed in the treatment of neuroendocrine tumors (NET), where somatostatin analogs (DOTATATE) are radiolabeled with (90)Y, (68)Ga or (111)In for pre-therapeutic and therapeutic purposes. Quantitative evaluation of the biokinetic data can be performed by using physiologically based pharmacokinetic (PBPK) models. Knowledge about the biodistribution in a pre-clinical setting would allow optimizing the translation from bench to bedside. The aim of this study was to develop a PBPK model to describe the biodistribution of a novel sst2-targeting radiotracer.

METHODS

Biokinetic data of six mice after injection of (18)F-SiFAlin-Asp3-PEG1-TATE were investigated using two PBPK models. The PBPK models describe the biodistribution of the tracer in the tumor, kidneys, liver, remainder and whole body via blood flow to these organs via absorption, distribution, metabolism and excretion. A recently published sst2 PBPK model for humans (model 1) was used to describe the data. Physiological information in this model was adapted to that of a mouse. Model 1 was further modified by implementing receptor-mediated endocytosis (model 2). Model parameters were fitted to the biokinetic data of each mouse. Model selection was performed by calculating Akaike weights wi using the corrected Akaike Information Criterion (AICc).

RESULTS

The implementation of receptor-mediated endocytosis considerably improved the description of the biodistribution (Akaike weights w1=0% and w2=100% for model 1 and 2, respectively). The resulting time-integrated activity coefficients determined by model 2 were for tumor (0.05 ± 0.02) h, kidneys (0.11 ± 0.01) h and liver (0.02 ± 0.01) h.

CONCLUSION

Simply downscaling a human PBPK model does not allow for an accurate description of (18)F-SiFAlin-Asp3-PEG1-TATE in mice. Biokinetics of this tracer can be accurately and adequately described using a physiologically based pharmacokinetic model including receptor-mediated endocytosis. Thus, an optimized translation from bench to bedside is possible.

Dependence of treatment planning accuracy in peptide receptor radionuclide therapy on the sampling schedule

Background

Peptide receptor radionuclide therapy (PRRT) plays an important role in the treatment of neuroendocrine tumors (NET). Pre-therapeutic dosimetry using the area under the measured time-activity curve (AUC) is important. The sampling schedule for this dosimetry determines the accuracy and reliability of the obtained AUC.

The aim of this study was to investigate the effect of reduced number of measurement points (i.e., gamma camera image acquisition or serum measurements) on treatment planning accuracy in PRRT using ¹¹¹In-labeled-diethylenetriaminopentaacetic acid-octreotide (DTPAOC; Octreoscan™).

Methods

Pre-therapeutic biokinetic data of 15 NET patients were investigated using a recently developed physiologically based pharmacokinetic (PBPK) model. Two parameter sets were determined (standard or iterative approach) and used for calculation of time-integrated activity coefficients (TIACs) for the tumor, kidneys, liver, spleen, serum, and whole body. TIACs obtained using the full data sets were used as reference. To evaluate the effect of sampling on individual treatment planning, reduced sampling schedules were generated omitting either 1, 2, 3, or 4 organ and serum measurements or all serum measurements for each patient. Relative deviations (RDs) between these and reference TIACs were calculated and used as criterion for treatment planning accuracy. An RD < 0.1 was considered acceptable.

Results

When omitting serum measurements, TIAC accuracy remained acceptable (RD < 0.1) for the standard approach. The kidney TIACs could be estimated for both approaches with acceptable RDs using two time points (t = 4 h; 2 d); tumor RDs were <0.3. The iterative approach reduced the range of RD, but did not further reduce the number of needed measurement points (i.e., to achieve an RD <0.1). For both approaches RDs for liver, spleen and whole body were larger than 0.1. However, in the clinical setting these RDs are less relevant as liver and spleen are not organs at risk due to the low absorbed doses.

Conclusions

When using a priori information of a PBPK model structure combined with Bayesian information about PBPK model parameter distribution, the administered activity could be determined with acceptable accuracy using only two time points (4 h, 2 d) and thus allow a considerable reduction of needed data for individual dosimetry.