Quantitative 68Ga-DOTATATE PET/CT Parameters for the Prediction of Therapy Response in Patients with Progressive Metastatic Neuroendocrine Tumors Treated with 177Lu-DOTATATE

The aim of this study was to determine whether quantitative PET parameters on baseline 68Ga-DOTATATE PET/CT and interim PET (iPET) performed before the second cycle of therapy are predictive of the therapy response and progression-free survival (PFS). Methods: Ninety-one patients with well-differentiated neuroendocrine tumors (mean Ki-67 index, 8.3%) underwent 68Ga-DOTATATE PET/CT to determine suitability for peptide receptor radionuclide therapy as part of a prospective multicenter study. The mean follow-up was 12.2 mo. Of the 91 patients, 36 had iPET. The tumor metrics evaluated were marker lesion-based measures (mean SUVmax and ratio of the mean lesion SUVmax to the SUVmax in the liver or the SUVmax in the spleen), segmented 68Ga-DOTATATE tumor volumes (DTTVs), SUVmax and SUVmean obtained with the liver and spleen as thresholds, and heterogeneity parameters (coefficient of variation, kurtosis, and skewness). The Wilcoxon rank sum test was used for the association between continuous variables and the therapy response, as determined by the clinical response. Univariable and multivariable Cox proportional hazards models were used for the association with PFS. Results: There were 71 responders and 20 nonresponders. When marker lesions were used, higher mean SUVmax and ratio of the mean lesion SUVmax to the SUVmax in the liver were predictors of the therapy response (P = 0.018 and 0.024, respectively). For DTTV parameters, higher SUVmax and SUVmean obtained with the liver as a threshold and lower kurtosis were predictors of a favorable response (P = 0.025, 0.0055, and 0.031, respectively). The latter also correlated with a longer PFS. The iPET DTTV SUVmean obtained with the liver as a threshold and the ratio of mean SUVmax obtained from target lesions at iPET to baseline PET correlated with the therapy response (P = 0.024 and 0.048, respectively) but not PFS. From the multivariable analysis with adjustment for age, primary site, and Ki-67 index, the mean SUVmax (P = 0.019), ratio of the mean lesion SUVmax to the SUVmax in the liver (P = 0.018), ratio of the mean lesion SUVmax to the SUVmax in the spleen (P = 0.041), DTTV SUVmean obtained with the liver (P = 0.0052), and skewness (P = 0.048) remained significant predictors of PFS. Conclusion: The degree of somatostatin receptor expression and tumor heterogeneity, as represented by several metrics in our analysis, were predictive of the therapy response or PFS. Changes in these parameters after the first cycle of peptide receptor radionuclide therapy did not correlate with clinical outcomes.

First-in-Humans Application of 161Tb: A Feasibility Study Using 161Tb-DOTATOC

161Tb has decay properties similar to those of 177Lu but, additionally, emits a substantial number of conversion and Auger electrons. The aim of this study was to apply 161Tb in a clinical setting and to investigate the feasibility of visualizing the physiologic and tumor biodistributions of 161Tb-DOTATOC. Methods:161Tb was shipped from Paul Scherrer Institute, Villigen-PSI, Switzerland, to Zentralklinik Bad Berka, Bad Berka, Germany, where it was used for the radiolabeling of DOTATOC. In 2 separate studies, 596 and 1,300 MBq of 161Tb-DOTATOC were administered to a 35-y-old male patient with a metastatic, well-differentiated, nonfunctional malignant paraganglioma and a 70-y-old male patient with a metastatic, functional neuroendocrine neoplasm of the pancreatic tail, respectively. Whole-body planar γ-scintigraphy images were acquired over a period of several days for dosimetry calculations. SPECT/CT images were reconstructed using a recently established protocol and visually analyzed. Patients were observed for adverse events after the application of 161Tb-DOTATOC. Results: The radiolabeling of DOTATOC with 161Tb was readily achieved with a high radiochemical purity suitable for patient application. Planar images and dosimetry provided the expected time-dependent biodistribution of 161Tb-DOTATOC in the liver, kidneys, spleen, and urinary bladder. SPECT/CT images were of high quality and visualized even small metastases in bones and liver. The application of 161Tb-DOTATOC was well tolerated, and no related adverse events were reported. Conclusion: This study demonstrated the feasibility of imaging even small metastases after the injection of relatively low activities of 161Tb-DOTATOC using γ-scintigraphy and SPECT/CT. On the basis of this essential first step in translating 161Tb to clinics, further efforts will be directed toward the application of 161Tb for therapeutic purposes.

Utility of 18F-AlF-NOTA-Octreotide PET/CT in the Localization of Tumor-Induced Osteomalacia

CONTEXT

Tumor-induced osteomalacia (TIO) is a paraneoplastic disorder, usually caused by benign mesenchymal tumors that produce high levels of fibroblast growth factor 23. The only curative therapy is resection of the causative tumors.

OBJECTIVE

This research was conducted to evaluate the efficacy of 18F-AlF-NOTA-octreotide (18F-OC) positron emission tomography/computed tomography (PET/CT) in detecting TIO and its impact on patient management.

METHODS

Retrospective analysis was conducted of 17 patients with hypophosphatemic osteomalacia suspected to be TIO. A  18F-OC PET/CT study was performed in all 17 patients to localize the tumor and 68Ga-DOTATATE PET/CT was performed in 4 out of 17 patients; both studies were performed within 1 week of each other. Both studies were interpreted blindly without the knowledge of other imaging findings. The image findings were compared with the results of histopathological examinations and clinical follow-ups.

RESULTS

The 18F-OC PET/CT scans were positive in 14 patients. Furthermore, 4 of 14 patients were scanned with both 18F-OC and 68Ga-DOTATATE PET/CT. Both studies were able to localize the tumor in all 4 patients. In total, 14 patients had surgery to remove the lesions. Postsurgical pathological examination confirmed causative tumors in these patients, whose symptoms diminished promptly. Serum phosphate levels normalized, confirming the diagnosis of TIO. 18F-OC PET/CT sensitivity, specificity, and accuracy were 87.5%, 100%, and 88.2% respectively. 18F-OC PET/CT findings affected patient management in 88.2% of cases.

CONCLUSION

18F-OC PET/CT scan is useful in the detection of tumors causing TIO. Further studies with larger patient populations are needed to validate the result.

Prostate Cancer With Neuroendocrine Differentiation Recurring After Treatment With 177Lu-PSMA: A Chance for 177Lu-DOTATATE Therapy?

ABSTRACT

Prostate cancer with NED (neuroendocrine differentiation) may occur in various stages of the disease, which is associated with a poor prognosis and treatment resistance. We present a case of a patient with metastatic castration-resistant prostatic cancer, who was treated with 7 cycles of 177Lu-PSMA and a very good response. Although only few foci with PSMA uptake were remained in the last posttreatment images, PSA levels dramatically began to rise. This raised suspicion for NED, and 68Ga-DOTATATE was done showing sufficient uptake to consider a trial of 177Lu-DOTATATE. The patient reported pain response, and PSA levels dropped after 1 cycle of the treatment.

Addition of 131I-MIBG to PRRT (90Y-DOTATOC) for Personalized Treatment of Selected Patients with Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for metastatic neuroendocrine tumors. Delivering a sufficient tumor radiation dose remains challenging because of critical-organ dose limitations. Adding 131I-metaiodobenzylguanidine (131I-MIBG) to PRRT may be advantageous in this regard. Methods: A phase 1 clinical trial was initiated for patients with nonoperable progressive neuroendocrine tumors using a combination of 90Y-DOTATOC plus 131I-MIBG. Treatment cohorts were defined by radiation dose limits to the kidneys and the bone marrow. Subject-specific dosimetry was used to determine the administered activity levels. Results: The first cohort treated subjects to a dose limit of 1,900 cGy to the kidneys and 150 cGy to the marrow. No dose-limiting toxicities were observed. Tumor dosimetry estimates demonstrated an expected dose increase of 34%-83% using combination therapy as opposed to 90Y-DOTATOC PRRT alone. Conclusion: These findings demonstrate the feasibility of using organ dose for a phase 1 escalation design and suggest the safety of using 90Y-DOTATOC and 131I-MIBG.

Neuroblastoma xenograft models demonstrate the therapeutic potential of 177Lu-octreotate

BACKGROUND

Neuroblastoma (NB) is one of the most frequently diagnosed tumors in infants. NB is a neuroendocrine tumor type with various characteristics and features, and with diverse outcome. The most malignant NBs have a 5-year survival rate of only 40-50%, indicating the need for novel and improved treatment options. 177Lu-octreotate is routinely administered for treatment of neuroendocrine tumors overexpressing somatostatin receptors (SSTR). The aim of this study was to examine the biodistribution of 177Lu-octreotate in mice bearing aggressive human NB cell lines, in order to evaluate the potential usefulness of 177Lu-octreotate for treatment of NB.

METHODS

BALB/c nude mice bearing CLB-BAR, CLB-GE or IMR-32 tumor xenografts (n = 5-7/group) were i.v. injected with 0.15 MBq, 1.5 MBq or 15 MBq 177Lu-octreotate and sacrificed 1 h, 24 h, 48 h and 168 h after administration. The radioactivity concentration was determined for collected tissue samples, tumor-to-normal-tissue activity concentration ratios (T/N) and mean absorbed dose for each tissue were calculated. Immunohistochemical (IHC) staining for SSTR1-5, and Ki67 were carried out for tumor xenografts from the three cell lines.

RESULTS

High 177Lu concentration levels and T/N values were observed in all NB tumors, with the highest for CLB-GE tumor xenografts (72%IA/g 24 h p.i.; 1.5 MBq 177Lu-octreotate). The mean absorbed dose to the tumor was 6.8 Gy, 54 Gy and 29 Gy for CLB-BAR, CLB-GE and IMR-32, respectively, p.i. of 15 MBq 177Lu-octreotate. Receptor saturation was clearly observed in CLB-BAR, resulting in higher concentration levels in the tumor when lower activity levels where administered. IHC staining demonstrated highest expression of SSTR2 in CLB-GE, followed by CLB-BAR and IMR-32.

CONCLUSION

T/N values for all three human NB tumor xenograft types investigated were high relative to previously investigated neuroendocrine tumor types. The results indicate a clear potential of 177Lu-octreotate as a therapeutic alternative for metastatic NB.

Peptide Receptor Radionuclide Therapy With 177Lu-DOTATATE for Symptomatic Control of Refractory Carcinoid Syndrome

CONTEXT

Peptide receptor radionuclide therapy (PRRT) with [Lutetium-177-DOTA0-Tyr3]octreotate (177Lu-DOTATATE) results in an increase of progression-free survival and quality of life in patients with progressive, well-differentiated neuroendocrine neoplasms (NENs).

OBJECTIVE

To study the effect of 177Lu-DOTATATE in patients with carcinoid syndrome and radiologically stable or newly diagnosed disease treated solely for the purpose of symptom reduction.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care hospital.

PATIENTS

Twenty-two patients with a metastatic midgut NEN, elevated urinary 5-hydroxyindolacetic acid excretion, and flushing and/or diarrhea despite treatment with a somatostatin analog, without documented disease progression.

INTERVENTION

PRRT with 177Lu-DOTATATE (intended cumulative dose: 29.6 GBq) with a primary aim to reduce symptoms.

RESULTS

After PRRT, mean bowel movement frequency (BMF) decreased from 6.1 ± 3.4 to 4.6 ± 3.6 per day (P = 0.009). Flushes decreased from 4.3 ± 2.9 to 2.4 ± 2.7 flushes per day (P = 0.002). A decrease of BMF of more than 30% occurred in 47% of patients with baseline BMF of 4 or more (n = 17). In patients with ≥2 episodes of flushing a day (n = 15), 67% of patients had more than 50% decrease of daily flushing. A decrease in urinary 5-hydroxyindolacetic acid excretion of more than 30% was seen in 56% of patients. The European Organization for Research and Treatment of Cancer-Core Module diarrhea subscale score showed a trend toward improvement by an average of 16.7 ± 33.3 points (P = 0.11).

CONCLUSION

PRRT with 177Lu-DOTATATE effectively reduced diarrhea and flushing in patients with carcinoid syndrome and can be considered for symptomatic treatment of carcinoid syndrome insufficiently controlled with somatostatin analogs.

Dissecting the target leukocyte subpopulations of clinically relevant inflammation radiopharmaceuticals

BACKGROUND

Leukocyte subtypes bear distinct pro-inflammatory, reparative, and regulatory functions. Imaging inflammation provides information on disease prognosis and may guide therapy, but the cellular basis of the signal remains equivocal. We evaluated leukocyte subtype specificity of characterized clinically relevant inflammation-targeted radiotracers.

METHODS AND RESULTS

Leukocyte populations were purified from blood- and THP-1-derived macrophages were polarized into M1-, reparative M2a-, or M2c-macrophages. In vitro uptake assays were conducted using tracers of enhanced glucose or amino acid metabolism and molecular markers of inflammatory cells. Both 18F-deoxyglucose (18F-FDG) and the labeled amino acid 11C-methionine (11C-MET) displayed higher uptake in neutrophils and monocytes compared to other leukocytes (P = 0.005), and markedly higher accumulation in pro-inflammatory M1-macrophages compared to reparative M2a-macrophages (P < 0.001). Molecular tracers 68Ga-DOTATATE targeting the somatostatin receptor type 2 and 68Ga-pentixafor targeting the chemokine receptor type 4 (CXCR4) exhibited broad uptake by leukocyte subpopulations and polarized macrophages with highest uptake in T-cells/natural killer cells and B-cells compared to neutrophils. Mitochondrial translocator protein (TSPO)-targeted 18F-flutriciclamide selectively accumulated in monocytes and pro-inflammatory M1 macrophages (P < 0.001). Uptake by myocytes and fibroblasts tended to be higher for metabolic radiotracers.

CONCLUSIONS

The different in vitro cellular uptake profiles may allow isolation of distinct phases of the inflammatory pathway with specific inflammation-targeted radiotracers. The pathogenetic cell population in specific inflammatory diseases should be considered in the selection of an appropriate imaging agent.

A Novel Time-Activity Information-Sharing Approach Using Nonlinear Mixed Models for Patient-Specific Dosimetry with Reduced Imaging Time Points: Application in SPECT/CT After 177Lu-DOTATATE

Multiple-time-point SPECT/CT imaging for dosimetry is burdensome for patients and lacks statistical efficiency. A novel method for joint kidney time-activity estimation based on a statistical mixed model, a prior cohort of patients with complete time-activity data, and only 1 or 2 imaging points for new patients was compared with previously proposed single-time-point methods in virtual and clinical patient data. Methods: Data were available for 10 patients with neuroendocrine tumors treated with 177Lu-DOTATATE and imaged up to 4 times between days 0 and 7 using SPECT/CT. Mixed models using 1 or 2 time points were evaluated retrospectively in the clinical cohort, using the multiple-time-point fit as the reference. Time-activity data for 250 virtual patients were generated using parameter values from the clinical cohort. Mixed models were fit using 1 (∼96 h) and 2 (4 h, ∼96 h) time points for each virtual patient combined with complete data for the other patients in each dataset. Time-integrated activities (TIAs) calculated from mixed model fits and other reduced-time-point methods were compared with known values. Results: All mixed models and single-time-point methods performed well overall, achieving mean bias < 7% in the virtual cohort. Mixed models exhibited lower bias, greater precision, and substantially fewer outliers than did single-time-point methods. For clinical patients, 1- and 2-time-point mixed models resulted in more accurate TIA estimates for 94% (17/18) and 72% (13/18) of kidneys, respectively. In virtual patients, mixed models resulted in more than a 2-fold reduction in the proportion of kidneys with |bias| > 10% (6% vs. 15%). Conclusion: Mixed models based on a historical cohort of patients with complete time-activity data and new patients with only 1 or 2 SPECT/CT scans demonstrate less bias on average and significantly fewer outliers when estimating kidney TIA, compared with popular reduced-time-point methods. Use of mixed models allows for reduction of the imaging burden while maintaining accuracy, which is crucial for clinical implementation of dosimetry-based treatment.

Characterisation of 99mTc EDDA/HYNIC-TOC (Tektrotyd) physiological and neuroendocrine tumour uptake using SPECT/CT standardised uptake values: initial experience

99mTc Ethylene diamine N,N'-diacetic acid hydrazinonicotinamide-conjugated Tyr3-octreotide (99mTc EDDA/HYNIC-TOC) single photon emission tomography/computed tomography (SPECT/CT) imaging of somatostatin receptors is used in the assessment of neuroendocrine tumours (NETs). The objective of this study was to characterise quantitative standardised uptake value (SUV) SPECT/CT of normal physiological uptake and NET disease. Forty-four patients (22 female and 22 male) referred for 99mTc EDDA/HYNIC-TOC SPECT/CT imaging for diagnosis/primary staging (n = 28) or the assessment of residual/recurrent disease (n = 16) were included. SPECT/CT SUVmax values were determined for normal physiological uptake (spleen, kidney, liver and bone) and NET disease (liver metastases, metastatic lymph nodes, bone metastases and intrapulmonary lesions). Statistical testing was performed to compare normal uptake and NET disease uptake in liver and bone (Student's t-test). The highest normal physiological uptake was observed in the spleen (mean SUVmax 29.8, SD 13.7), with lower uptake in the kidneys (16.7, 3.2) and liver (7.3, 2.1). Increased SUVmax values were observed in primary tumour and metastatic disease, greatest in liver metastases (21.8, 13.3), with lower, similar values obtained for metastatic lymph nodes (16.3, 7.5) and intrapulmonary lesions (17.5, 16.8). SUVmax in bone metastases averaged 12.9 (7.0). Significant differences were observed between normal and metastatic SUVmax in the liver and bone (P < 0.01). SPECT/CT SUV quantification is feasible in a manner similar to PET/CT. 99mTc EDDA/HYNIC-TOC SPECT/CT SUVmax has been characterised in NET disease, demonstrating high target to non-target ratios for primary tumours and metastatic lesions.

Rapid Progression After 177Lu-DOTATATE in Patients With Neuroendocrine Tumors

ABSTRACT

Peptide receptor radionuclide therapy (PRRT) is a treatment option for somatostatin receptor-positive, unresectable or metastatic neuroendocrine tumors (NETs). Despite high disease control rates seen with PRRT, a subset of the NET population seems to have a short progression-free interval. We hypothesize that patients with NETs with rapid progression post-PRRT may have mixed low- and high-grade cell populations, and PRRT treats the lower-grade component, allowing the more aggressive high-grade component to progress.We report 7 patients with biopsy-proven NET who received PRRT with 177Lu-DOTATATE at the Stanford Cancer Center who had evidence of progressive disease (PD) on or within 6 months of therapy.All patients had primary pancreatic, metastatic, well-differentiated NET on diagnosis and were heavily pretreated before receiving PRRT. Two patients had PD while on PRRT; 5 had PD within 6 months of completing PRRT. The median time from the last cycle to PD was 3.2 months (range, 1.1-4.6 months). The median progression-free survival was 7.7 months (95% confidence interval, 5.7-9.8 months). Three patients had a repeat biopsy post-PRRT, 2 of which demonstrated higher disease grade compared with their initial pathology. Further evaluation in larger patient cohorts is warranted to elucidate predictive factors of PRRT response/nonresponse to enable better patient selection.

Feasibility and Therapeutic Potential of Combined Peptide Receptor Radionuclide Therapy With Intensive Chemotherapy for Pediatric Patients With Relapsed or Refractory Metastatic Neuroblastoma

BACKGROUND

Recent evidence has demonstrated high expression of somatostatin receptors in neuroblastoma (NB) cells. Because of this, we endeavored to evaluate the diagnostic performance and clinical efficacy of 68Ga-DOTATATE PET/CT and peptide receptor radionuclide therapy (PRRT) using 177Lu-DOTATATE combined with chemotherapy in pediatric NB patients.

PATIENTS AND METHODS

In total, 14 pediatric patients with histopathologically confirmed NB underwent 68Ga-DOTATATE PET/CT. Among them, the patients who were refractory or relapsed after therapy with 131I-MIBG and had intensive uptake of 68Ga-DOTATATE were referred for PRRT using 177Lu-DOTATATE. Treatment response based on follow-up imaging was classified into complete response, partial response, stable disease, and progressive disease. After each cycle of PRRT, laboratory tests were performed for evaluation of hematological, renal, and hepatic toxicities. The CTCAE (Common Terminology Criteria for Adverse Events; version 4.03) was used for grading adverse event. Curie score and International Society of Pediatric Oncology Europe Neuroblastoma score were used for semiquantitative analysis of scans of patients who underwent PRRT. In addition, overall survival was calculated as the time interval between the date of the first cycle and the end of follow-up or death.

RESULTS

Overall, 14 refractory NB children including 7 boys and 7 girls with a median age of 5.5 years (ranged from 4 to 9) underwent 68Ga-DOTATATE PET/CT. PET/CT was positive in 10/14 patients (71.4%), and the median number of detected lesions in positive patients was 2 (range, 1-13). Of 14 patients, 5 patients underwent PRRT, including 3 boys and 2 girls. A total of 19 PRRT cycles and 66.4 GBq 177Lu-DOTATATE were given. Among these 5 patients, 2 showed an initial complete response, which relapsed a few months later, 1 showed a partial response, and 2 showed progressive disease. According to the Kaplan-Meier test, the overall survival was estimated at 14.5 months (95% confidence interval, 8.9-20.1). In evaluation of PRRT-related toxicity according to the CTCAE, 4 patients showed grade 1, and 1 showed grade 2 leukopenia. Two patients showed grade 1, and 2 others showed grade 2 anemia. Two patients showed grade 1, and 3 patients showed grade 2 thrombocytopenia. Serum creatinine in 1 patient increased to grade 1.

CONCLUSIONS

Combination of 177Lu-DOTATATE with chemotherapeutic agents might achieve worthwhile responses with low toxicity, encouraging survival in NB patients who have relapsed or are refractory to conventional therapy, including 131I-MIBG therapy. Imaging with 68Ga-DOTATATE PET/CT in such patients has a relatively high detection efficacy, demonstrating its potential use as an alternative imaging tool to conventional modalities such as 123I/131I-MIBG. However, further well-designed trials are highly warranted.

Long-term hematologic toxicity of 177Lu-octreotate-capecitabine-temozolomide therapy of GEPNET

Thirty-seven patients with advanced gastroenteropancreatic neuroendocrine tumors (GEPNETs) were treated on a prospective phase II single-center study with four cycles of 7.8 GBq 177Lu-octreotate combined with capecitabine and temozolomide chemotherapy (CAPTEM). Each 8-week cycle combined radiopeptide therapy with 14 days of capecitabine (1500 mg/m2) and 5 days of temozolomide (200 mg/m2). The incidence of grade ≥ 3 hematologic toxicity was analyzed. At a median follow-up of 7-years (range 1-10), six (16%) patients developed persistent hematologic toxicity (PHT) (defined as sustained grade ≥ 3 hematologic toxicity beyond 36-months follow-up) and three (8%) developed MDS/AL with a median time-to-event of 46 and 34 months, respectively. The estimated cumulative incidence of MDS/AL was 11% (95% CI: 3.45-24.01). Development of PHT was the only significant risk factor for secondary MDS/AL (RR, 16; 95% CI: 2.53 to 99.55; P < 0.001). The median PFS was 48 months (95% CI: 40.80-55.20), and the median OS was 86 months (95% CI: 56.90-115.13). Twenty-one deaths were recorded, including 13 (62%) due to progressive disease and all 3 (14%) patients with MDS/AL. 177Lu-octreotate CAPTEM therapy for GEPNETs is associated with a risk of long-term hematologic toxicity. The rising cumulative incidence of MDS/AL > 10% mandates the long-term monitoring of treated patients. However, time to onset is unpredictable, and incidence does not correlate with conventional baseline risk factors. Novel methods are required for the stratification of prospective patients based on genetic risk.

68Ga-DOTATATE PET/CT Imaging of Refractory Pituitary Macroadenoma Invading the Orbit

ABSTRACT

In addition to gastroenteropancreatic neuroendocrine neoplasms, a wide variety of tumors express somatostatin receptors. Somatostatin receptor imaging, heavily utilized in neuroendocrine oncology, may also have utility in the diagnosis of other neoplasms and raises the possibility of potential therapeutic options. We describe the case of a 60-year-old man who underwent 68Ga-DOTATATE PET/CT, demonstrating an avid invasive pituitary macroadenoma. This mass was persistent and refractory despite traditional treatment options. Because of the avidity, 177Lu-DOTATATE therapy was offered, although not ultimately performed, demonstrating a potential treatment for challenging cases utilizing the principles of theranostics.

Pre- and postoperative 68 Ga-DOTATOC positron emission tomography for hormone-secreting pituitary neuroendocrine tumours

OBJECTIVES

Somatostatin receptors (SSTRs) are potential targets for detecting pituitary neuroendocrine tumours (PitNETs) that can be visualized effectively with ⁶⁸ Ga-labelled PET tracers. With this study, we have evaluated the diagnostic properties of such a tracer, ⁶⁸ Ga-DOTATOC, in patients with hormone-producing PitNETs before and after surgery.

DESIGN/METHODS

This prospective case-control study presents preoperative positron emission tomography (PET) and histopathological data in 18 patients with somatotroph (n = 8), corticotroph (n = 7) and thyrotroph (n = 3) PitNETs. Patients were scanned pre- and postoperatively with ⁶⁸ Ga-DOTATOC PET. For the postoperative part of the study, patients with gonadotroph tumours (n = 7) were also included. Fifteen pituitary healthy controls underwent the same protocol once. The maximum standard uptake value (SUV_max ) was analysed in manually outlined regions around the tumour in patients and around the pituitary gland in controls. specimens were collected during surgery in subjects for assessment of adenohypophyseal tumour cell type and the SSTR expression.

RESULTS

Thyrotroph tumours showed higher uptake (median SUV_max 41.1; IQR 37.4-60.0) and corticotroph tumours lower uptake (SUV_max 6.8; 2.6-9.3) than normal pituitary gland (SUV_max 13.8; 12.1-15.5). The uptake in somatotroph tumours (SUV_max 15.9; 11.6-19.7) was similar to the uptake in the pituitary gland. There was a strong correlation between SUV_max and SSTR2 expression (r = .75 (P < .01)). In the postoperative evaluation, PET was able to correlate tracer uptake with biochemical cure and noncure in patients with an abnormal postoperative magnetic resonance image and a preoperative tumour uptake SUV_max  > 13.8.

CONCLUSIONS

⁶⁸ Ga-DOTATOC PET can be used to detect thyrotroph tumours in the pre- and postoperative imaging assessment. Corticotroph tumours had a significantly lower uptake compared to the pituitary gland but without a distinct increased tumour uptake the clinical postoperative value is limited.

Diagnostic utility of Ga-68 DOTA-SSTR and F-18 FDG PET/CT in the detection of culprit tumours causing osteomalacia: a systematic review and meta-analysis

BACKGROUND

Tumour-induced osteomalacia (TIO) or oncogenic osteomalacia is a rare variant of paraneoplastic syndrome secondary to a small benign phosphaturic mesenchymal tumour that secretes phosphaturic substances. Complete tumour excision is often curative. However, the localization of these offending tumours has always remained a challenge because of their small size, slow-growing nature, and presence in atypical locations. We performed a systemic review and meta-analysis on the sensitivity and specificity of F-18 FDG PET/CT and Ga-68 DOTA-SSTR PET/CT to detect tumours causing osteomalacia.

METHODS

Pub Med, SCOPUS, the Cochrane Library and Web of Science were searched for articles on F-18 FDG and Ga-68 DOTA-SSTR PET/CT in the detection of culprit tumours in TIO till September 2020. Both retrospective and prospective studies having three or more patients were included. The methodological quality of included studies was assessed using the Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies-2 checklist. A random-effect model was used for the statistical pooling of sensitivity and specificity. Pooled data were presented with 95% confidence intervals (95% CI) and displayed using Forest plots. Heterogeneity was expressed using the I2 statistic.

RESULTS

The pooled sensitivity of Ga-68 DOTA-SSTR PET/CT in detecting the culprit tumour derived from all included studies is 86% (95% CI: 79-91%). There is moderate statistical heterogeneity among the included studies (I2 = 72.7%). The pooled sensitivity of F-18 FDG PET/CT in detecting the offending tumour derived from all included studies is 73% (95% CI: 61-84%) with moderate statistical heterogeneity among the included studies (I2 = 45.4%).

CONCLUSION

In the detection of offending tumours in TIO, Ga-68 DOTA-SSTR PET/CT has better sensitivity than F-18 FDG PET/CT and should be used as first-line imaging modality due to very high sensitivity.

Patient external dose rate after 177Lu-DOTATATE therapy: factors affecting its decrease and predictive value

Rationale: Peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE (oxodotreotide) results in external radiation exposure from the patient. In the PREELU observational prospective study, we determined the equivalent dose rate at 1 m of the patient (EDR-1m) for a period following PRRT. The main objective was to predict which patients could be discharged from the hospital at approximately 3 h after the administration of 177Lu-DOTATATE, i.e. at the end of the infusion of amino-acids according to our PRRT protocol. As presenting no undue risk of radiation exposure for the public, those patients could be treated as outpatients or day patients, rather than inpatients. Methods: We sequentially measured EDR-1m facing the sternum and then the pelvis during 50 PRRT in 24 patients with metastatic neuroendocrine tumours, each 30 minutes after ending administration of Lutathera, over at least 180 minutes. Results: 180 minutes after the administration of ca. 7400 MBq of Lutathera, EDR-1m was <40 µSv/h in all cases, and <25 µSv/h in 32 cases (64%). After an overnight hospital stay, EDR-1m was <25 µSv/h in all cases. The EDR-1m value measured facing the sternum was the greatest in about one-fourth of paired measurements. In patients whose creatinine clearance was >96 mL/min/1.73m2, the EDR-1m was most likely (predictive value=90%) to drop below 25 µSv/h within 180 minutes after the administration of Lutathera. In 16 patients who benefited from several PRRT cycles, the creatinine clearance did not decrease significantly from one cycle to the next, probably due to the kidney protection by the amino-acid infusion. The patients whose EDR-1m dropped below 25 µSv/h at 180 minutes during their first PRRT cycle were unlikely (predictive value= 88%) to decease during the following two years. Conclusion: All patients could have been discharged 3 h after administration according to the criterion EDR-1m <40 µSv/h. Using EDR-1m <25 µSv/h as criterion, an extended hospital stay beyond 3 h would have been necessary in around one-third of the PRRT treatments and could be anticipated based on creatinine clearance ≤96 mL/min/1.73m2. EDR-1m <25 µSv/h at 180 min during the first PRRT yielded a strong predictive value on the patient's survival at two years, a finding that should be confirmed in future studies.

Investigating intrinsic radiosensitivity biomarkers to peptide receptor radionuclide therapy with [177Lu]Lu-DOTATATE in a panel of cancer cell lines

INTRODUCTION

[177Lu]Lu-DOTATATE is an effective systemic targeted radionuclide therapy for somatostatin receptor (SSTR) positive metastatic or inoperable neuroendocrine tumours (NET). However, for a given injected activity, tumour responses are variable. Our aim was to investigate whether SSTR expression/functionality and known characteristics of intrinsic radiosensitivity, namely proliferation rate, glucose metabolism, cell cycle phase, DNA repair and antioxidant defences were predictors of sensitivity to [177Lu]Lu-DOTATATE in SSTR expressing human cancer cell lines.

METHODS

In six human cancer cell lines and under basal condition, SSTR expression was assessed by qRT-PCR and immunocytochemistry. Its functionality was evaluated by binding/uptake assays with [68Ga]Ga- and [177Lu]Lu-DOTATATE. The radiosensitivity parameters were evaluated as follows: proliferation rate (cell counting), glucose metabolism ([18F]FDG uptake), antioxidant defences (qRT-PCR, colorimetric assay, flow cytometry), DNA repair (qRT-PCR) and cell cycle (flow cytometry). Effect of [177Lu]Lu-DOTATATE on cell viability was assessed 3, 7 and 10 days after 4 h incubation with [177Lu]Lu-DOTATATE using crystal violet.

RESULTS

Based on cell survival at day 10, cell lines were classified into two groups of sensitivity to [177Lu]Lu-DOTATATE. One group with <20% of survival decrease (-14 to -1%) and one group with >20% of survival decrease (-22 to -33%) compared to the untreated control cell lines. The latter had significantly lower total antioxidant capacity, glutathione (GSH) levels and glucose metabolism (p < 0.05) compared to the first group. SSTR (p = 0.64), proliferation rate (p = 0.74), cell cycle phase (p = 0.55), DNA repair (p > 0.22), combined catalase and GSH peroxidase expression (p = 0.42) and superoxide dismutase (SOD) activity (p = 0.41) were not significantly different between the two groups.

CONCLUSION

Antioxidant defences may be major determinants in [177Lu]Lu-DOTATATE radiosensitivity.

Feasibility and Therapeutic Potential of Peptide Receptor Radionuclide Therapy for High-Grade Gliomas

PURPOSE

This pilot study tested the principle that 177Lu-DOTATATE may be applied to patients with high-grade gliomas (HGGs) that are either inoperable or refractory to the standard conventional treatments and also assessed whether this approach could be a viable therapeutic plan in this dilemma.

METHODS

In this prospective study, 16 subjects experiencing HGGs that were either inoperable or refractory to the standard conventional treatments were included. All the patients checked for somatostatin receptor expression on the tumors. The patients were treated with 1 to 4 cycles of IV 177Lu-DOTATATE. The primary end point was radiological response after peptide receptor radionuclide therapy, and the secondary end point was improved quality of life using Karnofsky Performance Score and Eastern Cooperative Oncology Group score.

RESULTS

In total, 16 subjects (10 males and 6 females) with a mean age of 55.68 ± 13.17 years (26-73 years) participated in the study. Of them, 8 patients were new HGG cases, and 8 patients had recurrent tumors. The participants' responses to treatments were complete remission in 12.5% of (n = 2), partial remission in 31.25% (n = 5), disease stability in 18.7% (n = 3), and disease progression in 37.5% (n = 6). In total, pretreatment and posttreatment Karnofsky Performance Score and Eastern Cooperative Oncology Group scores did not improved (P > 0.05). The patients were followed up from 1 month to 26 months (median, 3 months).

CONCLUSIONS

This preliminary result suggests that peptide receptor radionuclide therapy using 177Lu-DOTATATE may be associated with positive effects in patients with HGGs (grade III-IV). However, this approach should be evaluated in a more homogeneous group of patients with more favorable performance status.

Primary Neuroendocrine Neoplasia of the Liver

ABSTRACT

The presence of primary neuroendocrine tumors in the liver is still a matter of controversy. We present a case of a somatostatin-receptor-positive mass of the liver in the 68Ga-DOTATOC PET/CT. No other primary tumor was found after conventional imaging, endoscopically, and after liver-segment resection. Immunohistochemically, a constellation of findings was found to be compatible with a primary neuroendocrine neoplasm of the liver.

A Cyanine-Bridged Somatostatin Hybrid Probe for Multimodal SSTR2 Imaging in Vitro and in Vivo: Synthesis and Evaluation

Multimodal imaging probes have attracted the interest of ongoing research, for example, for the surgical removal of tumors. Modular synthesis approaches allow the construction of hybrid probes consisting of a radiotracer, a fluorophore and a targeting unit. We present the synthesis of a new asymmetric bifunctional cyanine dye that can be used as a structural and functional linker for the construction of such hybrid probes. 68 Ga-DOTATATE, a well-characterized radiopeptide targeting the overexpressed somatostatin receptor subtype 2 (SSTR2) in neuroendocrine tumors, was labeled with our cyanine dye, thus providing additional information along with the data obtained from the radiotracer. We tested the SSTR2-targeting and imaging properties of the resulting probe 68 Ga-DOTA-ICC-TATE in vitro and in a tumor xenograft mouse model. Despite the close proximity between dye and pharmacophore, we observed a high binding affinity towards SSTR2 as well as elevated uptake in SSTR2-overexpressing tumors in the positron emission tomography (PET) scan and histological examination.

Comparison of Nausea and Vomiting Associated With Amino Acid Formulations Coinfused With Peptide Receptor Radionuclide Therapy: Commercial Parenteral Nutrition Formulas Versus Compounded Arginine/Lysine

OBJECTIVES

Positively charged amino acids (AA) such as arginine/lysine are coinfused with radiolabeled somatostatin analogs to reduce rates of nephrotoxicity. In the phase 3 NETTER-1 trial, commercial AA formulations were used in association with 177Lu-DOTA-0-Tyr3-Octreotate (DOTATATE). These formulations were also used in an early-access program (EAP) before regulatory approval of 177Lu-DOTATATE. Our program transitioned to compounded l-arginine 2.5%/l-lysine 2.5% in 0.9% NaCl after commercial approval of 177Lu-DOTATATE. We sought to compare rates of nausea/vomiting with arginine/lysine versus commercial parenteral AA formulations.

METHODS

Rates of nausea/vomiting of all 20 EAP patients who received commercial AAs (15% Clinisol) were compared with the first 29 patients to receive 177Lu-DOTATATE after commercial approval and coinfused with arginine/lysine. Other parameters reviewed included infusion rates, need for PRN nausea medications, and other toxicities.

RESULTS

Seventeen percent of patients who received compounded arginine/lysine experienced nausea, compared with 100% of patients in the EAP group (P < 0.0001). Infusion-related reactions occurred in 3% of the arginine/lysine cohort versus 35% in the EAP group. Infusion durations were substantially shorter in the arginine/lysine cohort (reduced by 61%).

CONCLUSIONS

Coinfusions of arginine/lysine with radiolabeled somatostatin analogs result in substantially lower rates of nausea/vomiting compared with commercial AA formulations designed for parenteral nutrition.

A combination of surgery, theranostics, and liquid biopsy - a personalised oncologic approach to treatment of patients with advanced metastatic neuroendocrine neoplasms

Rationale: Neuroendocrine neoplasia (NEN) of small bowel (SBNEN) frequently present with metastatic disease. Theranostics (molecular imaging followed by targeting therapy) allow for personalised medicine. Liquid biopsies enable precise identification of residual disease and real-time monitoring of therapeutic response. Our aim was to determine the clinical utility of a combination of surgery, theranostics, and a multigene blood measurement in metastasised SBNEN. Methods: Inclusion criteria were SBNEN, G1/G2 NEN, initial tumour diagnosis, stage IV NEN, positivity on 68Ga somatostatin analogue PET/CT, eligible for surgery, and 177Lu peptide receptor radionuclide therapy (PRRT). Blood samples for NETest were collected longitudinally. Progression-free survival (PFS) and overall survival (OS) were calculated. NETest results were assessed prior to surgery and during clinical follow-up. Results: A surgical cohort of 39 SBNEN patients met eligibility criteria. Thirty-two patients underwent ileal resection and 7 right hemicolectomy. The mean number of 177Lu PRRT cycles was 4. Mortality was nil. Surgical morbidity was 10.3%. Transient grade 1/2 toxicity occurred in 41% (PRRT). NETest scores (n=9 patients) decreased in 100% following treatment and correlated with diminished tumour volume and disease stabilization following surgery and PRRT. Median follow-up: 78 months. Median PFS and OS: 42.7 and 110 months, respectively. Progression-free survival at 1-, 3-, and 5-years was 79.4%, 57.1% and 40.5%, respectively. Overall survival at 1-, 3-, and 5-years was 97.4%, 97.4%, and 94.1%, respectively. Conclusions: Surgery combined with 177Lu PRRT is safe and provides favourable PFS and OS in selected patients with advanced SBNEN. Liquid biopsy (NETest) has the potential to accurately delineate disease status.