Cutaneous, Subcutaneous, and Bilateral Adrenal Gland Metastases in Progressive Prostate Carcinoma: Theranostic Potential of 68 Ga-PSMA-11 PET/CT Imaging and 177 Lu-PSMA-617 Therapy

ABSTRACT

Prostate carcinoma (PC) is the second most common malignant tumor in males globally. The metastatic spread of PC usually involves the pelvic and abdominal lymph nodes and the skeletal system. Cutaneous metastases are exceedingly uncommon and typically manifest themselves late in the disease course, considered as ominous sign with limited treatment options and a poor prognosis. We describe a patient wherein 68 Ga-PSMA-11 PET/CT detected multiple uncommon metastatic sites in the cutaneous region of the scrotum, penis, and thigh, as well as in the subcutaneous region of anterior abdominal wall, and in bilateral adrenal glands. These findings served as a theranostic tool for selecting 177 Lu-PSMA-617 treatment for these extremely rare metastatic sites.

Clinical Internal Dosimetry and Biodistribution of 177 Lu-DOTA-Trastuzumab in HER2-Positive Metastatic and Locally Advanced Breast Carcinoma

OBJECTIVE

The aim of this study was to assess the biodistribution and dosimetry of 177 Lu-DOTA-trastuzumab in patients with HER2-positive breast carcinoma using whole-body (WB) planar imaging at multiple time points.

PATIENTS AND METHODS

This study was a prospective evaluation of HER2-positive metastatic/locally advanced breast carcinoma patients who underwent gamma camera imaging for dosimetry and biodistribution studies by using 177 Lu-DOTA-trastuzumab. The standard diagnostic dosimetry protocol was followed, which included cold trastuzumab injection followed by in-house produced 177 Lu-DOTA-trastuzumab. Serial WB planar images (anterior and posterior) were obtained on gamma camera after the infusion of 177 Lu-DOTA-trastuzumab at multiple time points. Whole-body and organ regions of interest were drawn, and the numbers of disintegrations were obtained. The mean absorbed doses for the liver, spleen, kidneys, heart, red marrow, and tumor were obtained from OLINDA EXM v2.1.1 and ORIGIN software.

RESULTS

The study included a cohort of 21 female breast carcinoma patients. Tracer activity ( 177 Lu-DOTA-trastuzumab) was noted in the physiological organs such as the liver, spleen, kidneys, heart, as well as in the tumors. On visual analysis of 177 Lu-DOTA-trastuzumab biodistribution, the liver activity showed gradual clearance over time, and although spleen was comparatively faintly visualized than liver and similarly, kidneys were faintly visualized suggestive of the alternate route of tracer excretion. The maximum number of patients (n = 12) showed 2 components of clearance, namely, fast and slow. The average effective half-life of all the patients (including single and 2 components of clearance) was 106.25 ± 22.14 hours (84.11-128.39 hours). The mean absorbed dose for the liver, spleen, kidneys, heart, whole body, and red marrow was 1.0702 ± 0.731, 1.4114 ± 0.462, 1.4232 ± 0.364, 1.4719 ± 0.602, 0.2412 ± 0.0295, and 0.1485 ± 0.0213 mGy/MBq, respectively, by OLINDA EXM and 0.5741 ± 0.333, 0.8096 ± 0.224, 0.7943 ± 0.235, 1.8971 ± 0.713, and 0.09619 ± 0.0144 for liver, spleen, kidneys, heart and whole body respectively by ORIGIN. The absorbed radiation dose for tumor was 1.94E+2 by OLINDA EXM software and 1.78E+2 by ORIGIN software. In this study, during and after infusion of 177 Lu-DOTA-trastuzumab, no major adverse effects were noted in any patient except 1 patient who had grade 1 nausea and managed conservatively by antiemetic drug.

CONCLUSIONS

The results of our study demonstrated expected and favorable biodistribution and dosimetry with 177 Lu-DOTA-trastuzumab in HER2-positive breast carcinoma patients. We noticed the mean absorbed dose to the normal organs within the limits of maximum tolerable dose, and also tumor dose was higher than the normal liver dose. Therefore, we conclude that 177 Lu-DOTA-trastuzumab radioimmunotherapy is feasible and a safe treatment option for treating HER2-positive breast carcinoma patients.

Evaluation of prostate-specific membrane antigen expression in locally advanced or metastatic breast carcinoma with 68 Ga-PSMA-11 positron-emission tomography/computed tomography imaging for potential theranostics

BACKGROUND AND AIM

Prostate-specific membrane antigen (PSMA) is ubiquitously expressed in tumor-associated neovasculature and may be a potential theranostic in many solid cancers, including breast carcinoma (BC). Herein, we analyzed the presence of PSMA in BC, through qualitative and quantitative parameters on 68 Ga-PSMA-11 positron-emission tomography/computed tomography (PET/CT), across various hormonal subtypes.

METHODS

This study examined 41 female patients of BC. All underwent 68 Ga-PSMA-11 PET/CT. For qualitative analysis, a visual estimation of PSMA expression was performed as per miPSMA scoring system (VISION trial) and a score ≥2 was considered eligible for lutetium-177 ( 177 Lu)-PSMA-617 radioligand therapy (Lu-PRLT). For quantitative analysis, maximum standardized uptake values (SUVmax) were determined and ratios >1 for SUVmax lesion to SUVmax liver were considered eligible for Lu-PRLT. PSMA expression was correlated with hormonal status using Chi-square test. The sensitivity, specificity and area under curve (AUC) of PSMA expression were determined using receiver-operating characteristics analysis ( P < 0.05).

RESULTS

A total of 19 patients (46.3%) and 15 patients (36.7%) in stage IV were found eligible for Lu-PRLT based on qualitative and quantitative analyses, respectively. Strong PSMA expression was detected in triple-negative and hormonal receptors-negative/human epidermal growth factor receptor 2-positive status on qualitative PSMA expression analysis. A sensitivity of 65.5%, specificity of 93.3% and AUC of 0.857 for SUVmax 6.5 on 68 Ga-PSMA-11 PET/CT were detected for PSMA expression for considering Lu-PRLT.

CONCLUSION

We found a modest number of BC patients suited for Lu-PRLT, indicating that PSMA PET/CT imaging may be a valuable modality for selecting theranostics in a carefully selected group of breast carcinoma.

Unusual Metastatic Sites of Testis and Rectum in Prostate Cancer Detected by 68 Ga-PSMA-11 PET/CT Imaging at Initial Staging

Imaging plays a pivotal role in defining the extent of disease and deciding therapeutic strategies in recently diagnosed high-risk prostate cancer. Standard-of-care conventional imaging may often miss rare metastatic disease sites. We herein present a unique case of prostate cancer where 68 Ga-PSMA-11 positron emission tomography (PET)/computed tomography (CT) detected two unusual metastatic sites (testis and rectum) in a single patient at initial staging, resulting in an accurate determination of the extent of disease, more tailored multimodal treatment planning, and exploration of the theragnostic potential.

Testicular Metastasis From Neuroendocrine Tumors: Imaging and Theranostics Through 68 Ga-DOTATATE PET/CT and 177 Lu-DOTATATE-Based Peptide Receptor Radionuclide Therapy

ABSTRACT

Neuroendocrine tumors (NETs) are rare neoplasms arising from enterochromaffin cells, which are predominantly noted in the gastrointestinal tract and lung; metastases of NETs to the testes in NET are further uncommon. Testicular NET usually has no symptoms and/or presents with painless swelling of the scrotum. Detection of testicular lesion can be challenging and frequently missed on conventional radiological imaging. We present testicular NET missed on conventional radiological imaging, where 68 Ga-DOTATATE PET/CT imaging detected the testicular lesion, and further evident on 177 Lu-DOTATATE-based post-peptide receptor radionuclide therapy theranostic imaging.

18F-FDG PET/CT Versus 68Ga-PSMA-11 PET/CT in Evaluation of Distant Metastatic Disease in Recurrent Renal Cell Carcinoma

Prostate-specific membrane antigen (PSMA) expression has been observed in the neovasculature of various malignancies. We present a case of metastatic renal cell carcinoma (RCC) with comparative 18F-FDG PET/CT and 68Ga-PSMA-11 imaging in which FDG PET/CT failed to detect metastatic thyroid disease and showed less 18F-FDG-concentrating lesions at other sites, whereas 68Ga-PSMA-11 PET/CT identified metastatic thyroid disease and demonstrated intensely 68Ga-PSMA-11-expressing distant metastatic lesions. 68Ga-PSMA-11 PET/CT may be considered a potentially useful imaging technique in RCC to detect metastasis and to guide the choice of specific treatments, such as PSMA-based radionuclide therapy in patients with recurrent metastatic RCC.

PSMA-targeted radioligand therapy in prostate cancer: current status and future prospects

INTRODUCTION

The prostate-specific membrane antigen (PSMA) targeted radioligand therapy (PRLT) for the treatment of metastatic castration-resistant prostate cancer (mCRPC) patients has generated significant interest among the oncologic community, with several publications documenting good response rates and survival benefits with low toxicity profiles.

AREAS COVERED

Indications, patient preparation, dose administration, post-treatment imaging, dosimetry, and side effect profiles of 177Lu-PSMA-617 are discussed in this article. We also discuss results from prospective studies, major retrospective studies, meta-analyses, clinical trials, and mentioned major ongoing clinical trials on PRLT. We have also portrayed our own experiences and future perspectives on PRLT.

EXPERT OPINION

For PRLT, PSMA-617 and PSMA-I&T molecules have revolutionized the theranostic approach in the management of advanced prostate cancer, with solid backing from several published articles showing favorable outcomes and an excellent safety profile of 177Lu-PSMA-617. Improvement in quality of life and survival was seen in the majority of mCRPC patients after 177Lu-PSMA-617 PRLT. Patients with good performance status, asymptomatic, only lymph node metastases, high PSMA expressing lesions, and no discordant FDG avid lesions have a longer survival after 177Lu-PSMA-617 PRLT than patients with poor performance status, symptomatic, hepatic, brain, and skeletal metastases, discordant PSMA, and FDG-avid lesions. Docetaxel and cabazitaxel are approved treatments for mCRPC patients. 177Lu-PSMA-617 is approved as a third-line systemic treatment for mCRPC patients with failure to respond to androgen receptor pathway inhibitors and docetaxel therapy. PRLT is a safe and effective alternative to cabazitaxel (third-line systemic treatment), but it has a higher cost. 177Lu-PSMA-617 could be a more efficient therapeutic option for mCRPC patients as first-line or combined therapy, and it may be a useful therapeutic option for the treatment of metastatic hormone-sensitive prostate cancer (mHSPC) patients. Several clinical studies and clinical trials on PRLT are currently underway. In the future, the results of these trials will be helpful in evolving treatment strategies for prostate cancer patients.

False-Positive 68Ga-DOTATATE PET/CT Findings in Hereditary Hypophosphatemia-Osteomalacia Mimicking Culprit Lesions of Tumor-Induced Osteomalacia

⁶⁸Ga-DOTATATE PET/CT is an important imaging modality for detection of culprit lesions of tumor-induced osteomalacia in clinically symptomatic patients with hypophosphatemia-osteomalacia. Somatostatin receptor expression may at times be observed in inflammatory or granulomatous conditions and in fractures or degenerative bone disease, leading to false-positive scan findings. We present a rare case of hereditary hypophosphatemia-osteomalacia that showed increased false-positive uptake (for possible tumor-induced osteomalacia lesions) in an inflammatory condition of the maxillary sinus and a fracture of the tibia on somatostatin receptor-based ⁶⁸Ga-DOTATATE PET/CT.

Imaging Recommendations for Theranostic PET-CT in Oncology

We in this article have presented a review of the guideline recommendations on theranostic positron emission tomography-computed tomography (PET-CT) imaging which will be helpful to assist practitioners in providing appropriate patient care. Multiple guidelines by different societies and medical associations provide standards for diagnosis, imaging, and treatment of cancer patients. They have generated a number of recommendations related to 68Ga-DOTATATE and 68Ga-PSMA-11 PET-CT, which are the classical examples of theranostic PET-CT imaging in current practice.

177 Lu-DOTATATE PRRT for Multiple Unusual Metastatic Sites in Neuroendocrine Tumor

ABSTRACT

Thyroid gland and orbit are rare sites of metastases in neuroendocrine tumors. We present an extremely rare case of rectal neuroendocrine tumor with metastases to thyroid gland and intra-orbital regions that demonstrated significant reduction in size and uptake of the lesions on somatostatin receptor based 68 Ga-DOTATATE PET/CT, following 177 Lu-DOTATATE peptide receptor radionuclide therapy. The case illustrates the efficacy of 177 Lu-DOTATATE peptide receptor radionuclide therapy for tumor cytoreduction, which can be considered as a promising treatment modality for somatostatin receptor expressing and tracer-avid metastatic lesions at multiple rare locations.

PET-CTBased Quantitative Parameters for Assessment of Treatment Response and Disease Activity in Cancer and Noncancerous Disorders

The various semiquantitative and quantitative PET-CT parameters provide measurement of disease activity and assessment of treatment response in the PET-CT studies. These include standardized uptake value (SUV), metabolic tumor volume (MTV) and total lesion glycolysis (TLG), and total metabolic tumor volume (TMTV). Thresholding and adaptive thresholding methods are commonly used algorithms for the evaluation of global disease activity. Readily available commercial software frequently in-built with the current generation PET-CT scanners for providing easy, less time consuming, highly reproducible, and more accurate measurement of global disease activity on PET-CT imaging in evaluation of malignant as well as benign disorders.

Thyroid Incidentaloma on 68Ga-PSMA-11 PET/CT Leading to Detection of Thyroid Metastasis in Metastatic Prostate Carcinoma

ABSTRACT

68Ga-labeled prostate-specific membrane antigen (PSMA)-11 PET/CT has evolved as the noninvasive imaging modality of choice in prostatic adenocarcinoma to detect overexpression of PSMA on prostate cancer cells. Metastasis to the thyroid gland is rarely observed in clinical practice of prostatic adenocarcinoma. Herein, we report the first and rare case of metastatic castration-resistant prostatic adenocarcinoma with thyroid metastasis. The patient demonstrated intensely PSMA-expressing primary prostatic lesion, metastatic lymph nodes, and skeletal lesions, and also mild uptake in thyroid nodule, which on further investigations was established as thyroid metastasis from prostate adenocarcinoma.

Combined 177 Lu-PSMA-617 PRLT and abiraterone acetate versus 177 Lu-PSMA-617 PRLT monotherapy in metastatic castration-resistant prostate cancer: An observational study comparing the response and durability

OBJECTIVE

The aim of present study was to determine and compare the overall response rates, progression-free survival (PFS), overall survival (OS), and clinical toxicity of the combination of 177Lu-PSMA-617 radioligand therapy (PRLT) and abiraterone acetate (AA) versus 177Lu-PSMA-617 PRLT as monotherapy in metastatic castration-resistant prostate cancer (mCRPC) patients.

MATERIALS AND METHODS

The mCRPC patients who received at least one cycle of ¹⁷⁷ Lu-PSMA-617 PRLT with or without AA therapy, were included and analyzed in the present study. The patients were divided into two major groups. Group 1 received only ¹⁷⁷ Lu-PSMA PRLT and Group 2 received combined ¹⁷⁷ Lu-PSMA PRLT + AA therapy. Therapeutic dose of ¹⁷⁷ Lu-PSMA-617 PRLT was 4.4-5.55 GBq per patient per cycle administered at intervals of 10-12 weeks in both groups. The Group 2 patients additionally received a dose of 1000 mg of AA once daily and 5 mg of prednisone twice daily. Treatment response in two groups was evaluated under four broad categories (a) symptomatic, (b) biochemical (serum prostate-specific antigen level), (c) objective molecular imaging (⁶⁸ Ga-PSMA-11 and ¹⁸ F-FDG PET/CT), and (d) objective anatomical imaging (computed tomography). For assessing treatment response, patients in two groups were categorized into responders (complete response [CR], partial response [PR], and stable disease [SD]) and nonresponders (progressive disease [PD]). The Kaplan-Meier product-limit method was used to calculate PFS and OS following first ¹⁷⁷ Lu-PSMA PRLT in the two groups. Univariate analysis was used to compare the patients' characteristics in two groups using a χ² or Fisher exact test. The Kaplan-Meier curves of PFS and OS between two groups were compared by using the log-rank test (p < 0.05 significant).

RESULTS

A total of 58 mCRPC patients (Group 1, 38 patients and Group 2, 20 patients) were included in this study analysis. The clinical and demographic characteristics of these patients (age, Gleason score, FDG avid disease, metastatic disease burden, and average number of ¹⁷⁷ Lu-PSMA PRLT cycles) in two groups were compared and found to be similar (p > 0.05). Post-treatment, symptomatic, biochemical, molecular, and anatomic imaging responders were found in 22 patients (58%) and 17 patients (85%), 22 patients (58%) and 16 patients (80%), 19 patients (54%) and 14 patients (78%), and 19 patients (54%) and 14 patients (78%) in Group 1 and Group 2, respectively. The median PFS of 7 months and median OS of 8 months were documented in Group 1, whereas median PFS was not reached and median OS of 16 months registered in Group 2. Transient hematological toxicity of Grades 1 and 2 was found in total seven patients (five patients in Group 1 and two patients in Group 2). On comparison of the treatment outcome between two groups, significant p value was found for symptomatic responders (58% in Group 1 vs. 85% in Group 2), median PFS (7 months in Group 1 vs. not reached in Group 2), and median OS (8 months in Group 1 vs. 16 months in Group 2), with better outcome in Group 2 patients for these variables.

CONCLUSION

In the present study, the combination of ¹⁷⁷ Lu-PSMA-617 PRLT and AA therapy showed significant improvement in mCRPC patients' symptomatic response, PFS, and OS as compared to ¹⁷⁷ Lu-PSMA-617 PRLT monotherapy.

Follicular thyroid carcinoma metastasizing to rare sites and exhibiting variable inter-lesional heterogeneity on 18F-fluorodeoxyglucose positron emission tomography/computed tomography and 131I

A patient of differentiated follicular thyroid carcinoma with unusual sites of metastases is illustrated with ¹³¹I and ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) imaging findings. The described case harbored extremely rare metastasis to the urinary bladder with multi-organ metastatic disease (including unusual sites of right bronchus and hepatic metastases). There was inter-lesional heterogeneity among the metastatic lesions with regard to the ¹³¹I and FDG uptake in the aforementioned lesions. The detection of such heterogeneity has important implications for patient management in metastatic differentiated thyroid carcinoma.

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.

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 indigenous 177Lu-DOTATATE PRRT in patients with Metastatic Advanced Neuroendocrine Tumours: a single institutional observation in a large tertiary care setting

OBJECTIVES

Assessment of long-term outcome and toxicity of indigenous ¹⁷⁷Lu-DOTATATE PRRT in patients of metastatic/advanced NETs in a large tertiary-care PRRT setting.

METHODS

A total of 468 metastatic/advanced NET patients (wide range of primary sites including CUP-NETs), who underwent at least two cycles of ¹⁷⁷Lu-DOTATATE PRRT with available follow-up information, were included and analysed retrospectively in this study. In-house labelling of DOTATATE with ¹⁷⁷Lu (direct route produced) was carried out in the hospital radiopharmacy and treatment administered in cycles (dose: 5.55 to 7.4 GBq per patient), at 10-12 weeks interval. The assessment of long-term outcome was undertaken under three broad headings: (a) Therapeutic response, (b) Survival outcome and (c) Toxicity assessment. The median point estimate with 95% CI for progression free survival (PFS) and overall survival (OS) were calculated by Kaplan-Meier method. Prognostic covariates for association with PFS and OS was investigated by Cox proportional hazards model (univariate and multivariate Hazard Ratios) and with disease control rate (DCR) by Chi-square test, with significant P value defined as <0.05.

RESULTS

Long-term outcome (follow-up ranging from 4 to 97.6 months; median period:46 months following first ¹⁷⁷Lu-DOTATATE PRRT) results showed, (i) on symptomatic response evaluation scale, complete response (CR) in 214 patients (45.7%), partial response (PR) in 108 (23.1%), stable disease (SD) in 118 (25.2%), progressive disease (PD) in 28 (6%). (ii) Biochemical response evaluation showed CR in 52 (12%), PR in 172 (40%), SD in 161 (38%), and PD in 42 patients (10%). (iii) Molecular imaging response (by PERCIST criteria) showed CR in 29 (6%), PR in 116 (25%), SD in 267 (57%) and PD in 56 (12%) patients. (iv) On RECIST 1.1 criteria, CR was observed in 14 patients (3%), PR in 126 patients (27%), SD in 282 patients (60%) and PD in 46 patients (10%). The median PFS and OS were not reached at a median follow-up of 46 months. Observed PFS and OS at 7 years were 71.1% 95% CI (62.4-79.7%) and 79.4% 95% CI (71.4-86.9%) respectively. PFS was dependent on previous history of chemotherapy, baseline ⁶⁸Ga-DOTATATE and ¹⁸F-FDG uptake, site of primary tumour, total cumulative dose and number of PRRT cycles on univariate analysis, whereas multivariate analysis showed significant association for previous history of chemotherapy, baseline ⁶⁸Ga-DOTATATE and ¹⁸F-FDG uptake and number of PRRT cycles. The OS was dependent on baseline ⁶⁸Ga-DOTATATE uptake, site of primary tumour, presence of bony metastatic disease, total cumulative dose and number of PRRT cycles on univariate analysis, whereas multivariate analysis showed significant association for bony metastatic disease and number of PRRT cycles. Transient haematological toxicity of Grade 1, Grade 2, and Grade 3 was found in 8 (1.7%), 1 (0.2%) and one patient (0.2%), respectively. Nephrotoxicity of Grade 1, Grade 2, Grade 3, and Grade 4 were seen in 16 (3.5%), 3 (0.6%), 2 (0.4%) and one patient (0.2%), respectively. On a separate sub-analysis of 322 NET patients with progressive disease at the initiation point of PRRT, overall response rates (CR + PR + SD) were 93.5%, 88.5%, 89.1 and 87.9% on symptomatic, biochemical, RECIST 1.1 and PERCIST criteria and PFS and OS at 7 years 68.3% and 79.2%, respectively.

CONCLUSIONS

The present results demonstrate that ¹⁷⁷Lu-DOTATATE PRRT improved symptoms and biochemical markers substantially in most of the NET patients, with disease stabilisation on both anatomical and molecular imaging in majority and response in a sizeable fraction. Additionally, the therapeutic protocol with lesser dose per cycle (mean 5.92 GBq/cycle) and prolonged duration (over 5 cycles and 1.5 years) in a metastatic NET setting proved equally efficacious (with superior PFS and OS rates) and relatively better tolerated with minimal toxicity.

ADVANCES IN KNOWLEDGE

The present work critically examines the long-term results, survival outcome and toxicity profile of the indigenous ¹⁷⁷Lu-DOTATATE (produced through direct neutron activation of enriched ¹⁷⁶Lu) in metastatic progressive NETs across a wide range of primary sites and malignancies. Such long-term outcome data establishes the favourable impact of PRRT in a wide patient base and also the therapeutic efficacy of the product.

Initial clinical evaluation of indigenous 90Y-DOTATATE in sequential duo-PRRT approach (177Lu-DOTATATE and 90Y-DOTATATE) in neuroendocrine tumors with large bulky disease: Observation on tolerability, 90Y-DOTATATE post- PRRT imaging characteristics (bremsstrahlung and PETCT) and early adverse effects

¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) alone has lesser potential in the clinical setting of neuroendocrine tumor (NET) with large bulky disease and nonhomogeneous somatostatin receptors (SSTR) distribution, owing to lower energy (Eβmax 0.497 MeV) and a shorter particle penetration range (maximum 2–4 mm) of ¹⁷⁷Lu. In large bulky NETs, ⁹⁰Yttrium (⁹⁰Y) has the theoretical advantages because of a longer beta particle penetration range (a maximum soft tissue penetration of 11 mm). Therefore, a combination of ¹⁷⁷Lu and ⁹⁰Y is a theoretically sound concept that can result in better response in metastatic NET with large-bulky lesion and non-homogeneous SSTR distribution. The aim of the study was to determine the feasibility of combining ⁹⁰Y-DOTATATE with ¹⁷⁷Lu-DOTATATE PRRT as sequential duo-PRRT in metastatic NET with (≥5 cm) including the post ⁹⁰Y-DOTATATE-PRRT imaging and also to determine early toxicity of the duo-PRRT approach. A total of 9 patients received combination of ¹⁷⁷Lu-DOTATATE with ⁹⁰Y-DOTATATE (indigenously prepared and approved) through sequential duo-PRRT approach. These 9 NET patients were included and analyzed in this study. All 9 patients had undergone post-PRRT ⁹⁰Y-DOTATATE imaging, including a whole-body planar bremsstrahlung imaging followed by regional single-photon emission computed tomography (SPECT)-computed tomography (CT) imaging and also a regional positron emission tomography–computed tomography imaging. Grading of ⁹⁰Y-DOTATATE and ¹⁷⁷Lu-DOTATATE uptake was done on post-PRRT imaging by both modalities. The size of the lesions ranged from 5.5 cm to 16 cm with average size of 10 cm before sequential duo-PRRT was decided. Sequential duo-PRRT was administered because of stable, unresponsive disease following ¹⁷⁷Lu-DOTATATE in 5 patients (55.6%), progressive disease after ¹⁷⁷Lu-DOTATATE in 2 patients (22.2%), and with neoadjuvant intent in 2 patients (22.2%). The total cumulative dose of ¹⁷⁷Lu-DOTATATE before duo-pRRT ranged from 11.84 GBq to 37 GBq per patient and average administered dose of 27.21 GBq per patient in this study. Out of 9 patients, 8 patients received single cycle of ⁹⁰Y-DOTATATE (ranging from 2.66 GBq to 3.4 GBq per patient with average administered dose of 3.12 GBq per patient). One patient received two cycles of ⁹⁰Y-DOTATATE (total dose of 6.2 GBq). Out of 9 patients, 8 patients showed excellent tracer concentration in lesions on post-PRRT ⁹⁰Y-DOTATATE imaging and the remaining 1 patient showed fairly adequate ⁹⁰Y-DOTATATE tracer uptake in lesion on visual analysis. There was matched ⁹⁰Y-DOTATATE uptake with ⁶⁸Ga-DOTATATE and also with ¹⁷⁷LuDOTATATE in all 9 patients. The sequential duo-PRRT was well tolerated by all patients. Two patients (22.2%) developed mild nausea, one patient (11.1%) developed transient mild-grade hemoglobin toxicity, and one patient (11.1%) developed mild-grade gastrointestinal symptoms (loose motion and abdominal pain). No nephrotoxicity, hepatotoxicity, and other hematological toxicity was observed. The combination of the indigenous ⁹⁰Y-DOTATATE with ¹⁷⁷Lu-DOTATATE PRRT in NET as sequential duo-PRRT was well tolerated, feasible and safe in stable, unresponsive/progressive disease following single isotope ¹⁷⁷Lu-DOTATATE therapy and also in neoadjuvant PRRT setting with large bulky lesion (≥≥5cm). Post-PRRT ⁹⁰Y-DOTATATE imaging showed excellent ⁹⁰Y-DOTATATE uptake in nearly all NET patients. Mild-grade early adverse effects were easily manageable and controllable in this sequential duo-PRRT approach.

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.

One decade of 'Bench-to-Bedside' peptide receptor radionuclide therapy with indigenous [177Lu]Lu-DOTATATE obtained through 'Direct' neutron activation route: lessons learnt including practice evolution in an Indian setting

The present treatise chronicles one decade of experience pertaining to clinical PRRT services in a large-volume tertiary cancer care centre in India delivering over 4,000 therapies, an exemplar of successful PRRT programme employing indigenous 177Lutetium production and resources. For the purpose of systematic discussion, we have sub-divided the communication into 3 specific parts: (a) Radiopharmaceutical aspects that describes 177Lutetium production through 'Direct' Neutron Activation Route and the subsequent radiolabeling procedures, (b) The specific clinical nuances and finer learning points (apart from the routine standard procedure) based upon clinical experience and how it has undergone practice evolution in our setting and (c) Dosimetry results with this indigenous product and radiation safety/health physics aspects involved in PRRT services. Initiated in 2010 at our centre, the PRRT programme is a perfect example of affordable quality health care delivery, with indigenous production of the radionuclide (177Lu) in the reactor and subsequent radiolabeling of the radiopharmaceutical ([177Lu]Lu-DOTATATE) at the hospital radiopharmacy unit of the centre, which enabled catering to the needs of a large number of patients of progressive, metastatic and advanced Neuroendocrine Neoplasms (NENs) and related malignancies.

Clinical efficacy of 177Lu-DOTATATE peptide receptor radionuclide therapy in thyroglobulin-elevated negative iodine scintigraphy: A "not-so-promising" result compared to GEP-NETs

This study aimed at assessing the performance of ¹⁷⁷Lu-DOTATATE-based peptide receptor radionuclide therapy (PRRT) in de-differentiated thyroid carcinoma thyroglobulin-elevated negative iodine scintigraphy (TENIS) in terms of clinical efficacy and outcome. This is a retrospective analysis of patients of TENIS who had undergone PRRT in a tertiary care setting. The selected patients were analyzed for the following parameters: (i) the patient characteristics, (ii) the metastatic burden, (iii) study of PRRT cycles and activity, (iv) response assessment (undertaken by three-parameter scale: symptomatic including Karnofsky/Lansky Performance scoring, biochemical and scan features) employing predefined criteria (detailed in methods), and (v) Grade III/IV hematological or renal toxicity. According to the qualitative uptake of the tracer in somatostatin receptor (SSTR)-based imaging (with either ^99mTc-HYNIC-TOC/⁶⁸Ga-DOTATATE), the lesions were divided into the following four categories: Grade 0: no uptake, Grade I: uptake less than the liver but more than background, Grade II: uptake equal to the liver, and Grade III: uptake more than the liver. A total of eight patients of TENIS who had undergone ¹⁷⁷Lu-DOTATATE were retrieved. Among those eight patients, the follow-up duration (from the time of the 1^st PRRT cycle) at the time of analysis ranged from 7 to 52 months, with an average of 34 months. At the time of assessment, two (25%) out of the eight patients had expired due to extensive metastatic disease and 6 (75%) were alive. On symptomatic response, complete disappearance of symptoms was found in one patient (12.5%), whereas three patients (37.5%) showed partial improvement in symptoms after PRRT and four patients (50%) showed worsening of and appearance of new symptoms. On biochemical response, reduction in serum thyroglobulin (TG) was found in three patients (37.5%) after PRRT and increase in serum TG was noticed in the rest of five patients (62.5%). Imaging response showed stable scan in two patients (25%) and progressive disease (PD) in six patients (75%), following a progression-free survival ranging from 7 to 16 months, when they were considered for tyrosine kinase inhibitors in view of PD. There was no obvious evidence of Grade III/IV hematological or renal toxicity in any of the patients, suggesting that the therapy in this group of patients is well tolerated. In addition, we also observed that most patients of TENIS showed low-grade uptake on SSTR-based imaging (Grade II as per our semi-quantitative scale), with only one patient showing Grade III uptake. ¹⁷⁷Lu-DOTATATE PRRT demonstrates modest response in SSTR-positive metastatic TENIS patients: (i) low SSTR expression and tracer avidity, and correspondingly lesser degree of targeting by the therapeutic agent and (ii) the fact that most of the TENIS patients usually have fluorodeoxyglucose (FDG)-avid disease, where high FDG avidity is commensurate with aggressive biology and could be the reason for the relatively less response documented. Larger prospective data need to be accrued in this domain in view of its well tolerability and nonavailability of better efficacious and less toxic treatment at present; however, this needs to be tried in receptor-positive cases with high-grade uptake (Score III/IV) for a definitive conclusion.

Therapeutic efficacy, prognostic variables and clinical outcome of 177Lu-PSMA-617 PRLT in progressive mCRPC following multiple lines of treatment: prognostic implications of high FDG uptake on dual tracer PET-CT vis-à-vis Gleason score in such cohort

OBJECTIVE

To evaluate the therapeutic response, progression free survival (PFS), overall survival (OS) and clinical toxicity of ¹⁷⁷Lu-PSMA-617 PSMA targeted radioligand therapy (PRLT) in the setting of heavily pre-treated metastatic castrate-resistant prostate cancer (mCPRC) patients and also examine the association of prognostic variables with therapeutic outcome in such patient cohort.

METHODS

We examined the medical records of mCRPC patients who had undergone ¹⁷⁷Lu-PSMA-617 PRLT from March 2017 to February 2019 in our institute. Patients receiving equal to or more than two cycles were included and analyzed in this retroprospective study.The ⁶⁸Ga-PSMA-11 PET-CT and 18-fludeoxyglucose positron emission tomography (¹⁸FDG PET)-CT scan findings, serum prostate-specific antigen (PSA) change, health-related quality of life (HRQoL) scales (Eastern Cooperative Oncology Group/Karnofsky score) and Gleason score were assessed for their implications on the outcome of therapy. The treatment response was evaluated under three categories: (a) symptomatic (b) biochemical and (c) imaging response.The PFS and OS following first PRLT were determined and the association of various variables with PSA doubling time (DT) and FDG uptake in the lesions were analyzed. Toxicity assessment was undertaken objectively by National Cancer Institute-Common Terminology Criteria for Adverse Events scale v. 5.0 for haematological and nephrotoxicity, and salivary gland toxicity assessed by xerostomia inventory score.

RESULTS

A total of 40 mCRPC patients (age range: 46-84 years; median 63 years), who had undergone ¹⁷⁷Lu-PSMA-617 PRLT, of at least two cycles was identified and selected for the analysis. FDG uptake was noted in 87.5% of patients (n = 35). Out of 40 cases, 21 were responders (CR, PR and SD) and 19 were non-responders (PD) on symptomatic and biochemical scales while on molecular imaging response, 16 (43%) were responders and remaining 21 (57%) were non-responders. Lesion-wise, ⁶⁸Ga-PSMA-11 avid metastatic nodal disease responded well with ¹⁷⁷Lu PSMA-617 PRLT, as compared to hepatic and skeletal lesions. The median OS and PFS was 12 and 7 months respectively following first PRLT. Patients with negative serum PSA-DT demonstrated superior 1 year PFS as compared to those with positive serum PSA-DT (52.5 vs 47.5%) (p = 0.029). Patients receiving greater than two cycles PRLT demonstrated a higher negative PSA-DT as compared to those receiving two cycles (p-value = 0.03). Grade 1 xerostomia was observed in two patients (5%) (mean xerostomia score of 23), haematotoxicity in seven patients [Grade I (n = 2, 5%) and Grade II (n = 5, 14%)].

CONCLUSION

¹⁷⁷Lu-PSMA-617 PRLT was well-tolerated and able to produce disease control with good symptomatic and biochemical responses in the context of heavily pre-treated mCRPC with progressive disease, with low toxicity profile. Evident association of high FDG uptake was observed with aggressive disease biology coupled with increasing Gleason score and poorer 12 months PFS. Negative PSA-DT following therapy demonstrated longer PFS. The results demonstrate important future role of ¹⁷⁷Lu-PSMA-617 PRLT in the treatment of mCRPC.

ADVANCES IN KNOWLEDGE

The present work explored in a large teriary cancer care setting, the efficacy of ¹⁷⁷Lu-PSMA-617 PRLT, in an aggressive and unselected subset of mCRPC. The response and outcome was correlated with a number of prognostic variables, including molecular imaging findings (FDG uptake in the metastatic lesions), PSA DT and Gleason score.

Prevalence of hitherto unknown brain meningioma detected on 68Ga-DOTATATE positron-emission tomography/computed tomography in patients with metastatic neuroendocrine tumor and exploring potential of 177Lu-DOTATATE peptide receptor radionuclide therapy as single-shot treatment approach targeting both tumors

There is a relative paucity of data in the literature regarding the prevalence of meningiomas and their detection in the clinical setting of neuroendocrine tumors (NETs). The primary aim of this study was to study incidentally detected meningiomas (on ⁶⁸Ga-DOTATATE/ ¹⁸F fluorodeoxyglucose positron-emission tomography/computed tomography [¹⁸F-FDG PET/CT]) in metastatic NET patients referred for peptide receptor radionuclide therapy (PRRT). The secondary aims of this study were to evaluate the response rate of these incidentally detected meningiomas following PRRT and determine progression-free survival (PFS) in this group of patients. This was a retrospective analysis of 500 metastatic/advanced NET patients who had undergone ⁶⁸Ga-DOTATATE PET/CT and ¹⁸F-FDG PET/CT before PRRT workup. The case records were searched to identify cases of hitherto unknown meningiomas detected on PET images; subsequently, these patients underwent brain magnetic resonance imaging (MRI) for confirmation of diagnosis. Following ¹⁷⁷Lu-DOTATATE PRRT, posttreatment functional and structural imaging response evaluation of the meningiomas were undertaken by ⁶⁸Ga-DOTATATE PET/CT, MRI, or CT brain, respectively, along with clinical neurological evaluation. The patients were designated as responders and nonresponders based on predefined response assessment criteria. The PFS of these incidentally detected meningiomas following PRRT was estimated using the Kaplan-Meier product-limit method. Twelve NET patients were retrospectively identified with abnormal focal brain uptake on ⁶⁸Ga-DOTATATE PET/CT. Of these, meningiomas were finally diagnosed on brain MRI examination in six patients (M: F =3:3; age range: 30-66 years; and mean age: 45 years), with a prevalence of 1.2%. Standardized uptake value (SUVmax) of meningiomas on ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT ranged from 7.0 to 22.0 (average 17.0) and 10.19-13.70 (mean: 12.10), respectively, and lesion-to-normal brain parenchyma SUVmax ratio ranged from 140 to 400 (mean: 340) and 1.02-1.07 (mean: 1.04), respectively. Of six patients with incidentally detected meningiomas, one patient died within 1 month and five patients received ¹⁷⁷Lu-DOTATATE PRRT, the number of cycles ranging from two to six (average: 4) and cumulative therapeutic dose ranging from 13.28 to 29.97GBq (average dose: 19.86GBq). Follow-up in these patients ranged from 8 to 36 months (mean: 19.4 months) after the first dose of PRRT. Complete disappearance of neurological symptoms was found in two of five patients (40%), partial response in one of five (20%), and worsening of symptoms in two of five patients (40%). The overall "responder" and "nonresponder" of the meningiomas after PRRT were three patients (60%) and two patients (40%), respectively. Two patients (40%) died of advanced NET at the time of analysis of these data. The observed mean PFS of the meningioma lesions following PRRT was 26.25 months (95% confidence interval, 16.65-35.84 months). No major hematological and renal toxicity were documented in any of these patients. To conclude, ⁶⁸Ga-DOTATATE PET/CT imaging is an effective technique for the incidental identification of meningioma in NET patients. Considering the limited therapeutic options in the palliative setting of advanced or metastatic NET patients and morbidity associated with the therapeutic procedures, PRRT could be a promising targeted therapeutic approach for such cases of incidentally detected meningiomas, which is also helpful in stabilizing the disease process without any significant toxicity.

Bilateral Orbital Soft-Tissue Metastases from Renal Neuroendocrine Tumor: Successful Theranostic Application of 68Ga/177Lu-DOTATATE with Improvement of Vision

A gratifying clinical response obtained in the setting of bilateral orbital metastases from renal neuroendocrine tumor is reported. Methods: A 53-y-old man diagnosed with renal neuroendocrine tumor (MIB1 index, 4%), with symptoms of skeletal and abdominal pain, proptosis, and a decrease in vision of the left eye, was found to harbor bilateral orbital soft-tissue lesions on ⁶⁸Ga-DOTATATE PET/CT and MRI in addition to widespread metastatic skeletal lesions and metastatic lymph nodal disease. Despite radiotherapy to the left eye (20 Gy) and long-acting octreotide therapy for 18 mo, his symptoms worsened, with an increase in serum chromogranin A level, and he was considered for ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT). Results: There was a significant improvement in skeletal pain, proptosis, and vision after 4 cycles of PRRT (cumulative dose of 22.2 GBq), stable disease on scanning, and a decrease in serum chromogranin A (from 150 to 36.39 ng/mL), with progression-free survival at 18 mo. Conclusion: PRRT through theranostic application of ⁶⁸Ga/¹⁷⁷Lu-DOTATATE was thus helpful in this uncommon clinical setting.

Dual-time point 18F-FDG-PET and PET/CT for Differentiating Benign From Malignant Musculoskeletal Lesions: Opportunities and Limitations

In this review, we summarize the false-positive and false-negative results of standard ¹⁸F-FDG-PET/CT in characterizing musculoskeletal lesions and discussed the added value and limitations of dual-time point imaging (DTPI) and delayed imaging in differentiating malignant from benign musculoskeletal lesions, based on review of the peer-reviewed literature. The quantitative and semiquantitative parameters adopted for DTPI are standardized uptake value (mainly maximum standardized uptake value [SUVmax]) and retention index (RI), calculated as RI (%) = 100% × (SUV [maxD-Delayed] - SUV [maxE-Early])/SUV [maxE-Early], although the criteria and cutoff for diagnosing malignancy in studies have varied considerably. Also, there has been considerable heterogeneity in protocol (time point of delayed imaging), interpretation, and results in dual-time point (DTP) ¹⁸F-FDG-PET for differentiating malignant from benign musculoskeletal lesions in various research studies. The specificity of DTPI is a function of many factors such as the nature of the musculoskeletal lesion or malignancy in question, the prevalence of false-positive etiologies in the patient population, and the cutoff values (either SUVmax or RI) employed to define a malignancy. Despite the apparent conflicting reports on the performance, there have been certain common points of agreement regarding DTPI: (1) DTP PET increases the sensitivity of ¹⁸F-FDG-PET/CT due to continued clearance of background activity and increasing ¹⁸F-FDG accumulation in malignant lesions, when the same diagnostic criteria (as in the initial standard single-time point imaging) are used. Increased sensitivity for lesion detection can be viewed as a strong point of DTP and delayed-time point imaging. (2) The causes for false positives (such as active infectious or inflammatory lesions and locally aggressive benign tumors) and false negatives (eg, low-grade sarcomas) are the major hurdles accounting for reduced diagnostic value of the technique, with overlap of ¹⁸F-FDG uptake patterns between benign and malignant musculoskeletal lesions on DTPI. (3) DTPI, however, could still be potentially useful in increasing the confidence of interpretation such as differentiating malignancy from sites of inactive or chronic inflammation, post-treatment viable residue vs necrosis, and certain other benign lesions. (4) Consideration of diagnostic CT component of PET/CT and the patient's clinical picture can lead to increase in specificity of interpretation in a given case scenario. Further systematic research, adoption of uniform protocol, and interpretation criterion could evolve the specific indications and interpretation criteria of DTPI for improved diagnostic accuracy in musculoskeletal lesions and its clinical applications.