Quantification of bone flare on 18F-NaF PET/CT in metastatic castration-resistant prostate cancer

Full-Body Tumor Response Heterogeneity of Metastatic Neuroendocrine Tumor Patients Undergoing Peptide Receptor Radiopharmaceutical Therapy

Patients with metastatic neuroendocrine tumors (NETs) can present with hundreds of lesions, and each lesion might have a unique response pattern to peptide receptor radiopharmaceutical therapy (PRRT). This response heterogeneity has been observed but is poorly understood. In this work, we perform a quantitative analysis of longitudinal PET/CT scans to comprehensively characterize the NET response to PRRT. Methods: NET patients treated with [177Lu]Lu-DOTATATE PRRT imaged at baseline, during, and after PRRT with [68Ga]Ga-DOTATATE PET/CT were enrolled in this retrospective single-institutional study. A deep-learning model was used to identify and contour regions of nonphysiological elevated tracer uptake (lesion-regions of interest [ROIs]). An automated analysis was performed to identify, contour, and quantify the individual lesion-ROI uptake, match ROI between time points, and categorize each lesion-ROI as disappearing, decreasing (ΔSUVtotal < -30%), stable (-30% ≤ ΔSUVtotal ≤ 30%), increasing (ΔSUVtotal > 30%), or new. A patient was considered to have response heterogeneity if both new or increasing lesion-ROIs and decreasing or disappearing lesion-ROIs were present after therapy. Results: Eighteen patients who received between 2 and 7 [68Ga]Ga-DOTATATE PET/CT scans were enrolled. In total, 3,289 lesion-ROIs were contoured in the 67 scans acquired (median of 24 lesion-ROIs per image), and 1,459 lesion-ROI tracks, defined as the path that each unique lesion-ROI follows across all time points, were determined by the ROI tracking method (median of 49 tracks per patient). All patients presented with disease response heterogeneity at the first follow-up scan. All 10 patients with more than 1 follow-up scan showed nonmonotonic change in lesion-ROI uptake. Of 129 tracks containing new lesion-ROIs at the first follow-up, 80 (62%) eventually resolved on final follow-up, whereas only 12% (7/60) of the tracks with lesion-ROIs disappearing at the first follow-up scan returned on final follow-up. Conclusion: To the best of our knowledge, this is the first study to evaluate response comprehensively and quantitatively in terms of individual lesion-ROIs. Response heterogeneity was observed in 100% of the patients, which suggests that comprehensive, lesion-level, response assessment is vital for the accurate understanding of the NET response to PRRT.

Flare phenomenon visualized by 99mTc-bone scintigraphy has prognostic value for patients with metastatic castration-resistant prostate cancer

OBJECTIVE

This study aimed to determine the prognostic value of the flare phenomenon in patients with metastatic castration-resistant prostate cancer (mCRPC) using the bone scan index (BSI) derived from 99mTc-methylenediphosphonate (MDP) bone scintigraphy images.

METHODS

We categorized 72 patients from the PROSTAT-BSI registry with mCRPC who were followed-up for 2 years after starting docetaxel chemotherapy to groups based on pre-chemotherapy BSI values of < 1, 1-4, and > 4. We assessed the effects of the flare phenomenon (defined as a > 10% increase in the BSI within 3 months of starting chemotherapy, followed by > 10% improvement within the next 3 months) on survival using Kaplan-Meier curves and Cox proportional hazard analyses.

RESULTS

The flare phenomenon was found in 26 (36%) of the 72 patients. Prostate-specific antigen (PSA), alkaline phosphatase (ALP), and hemoglobin (Hb) levels steadily increased, then deteriorated in patients with and without flare, respectively. Elevated BSI and PSA values at 3 months after starting therapy and the absence of abiraterone or/and enzalutamide therapy led to poor 2-year overall survival (OS) in the group without flare. In contrast, no influence was noticeable in the group with flare. The results of multivariable analyses that included only factors associated with PSA and BSI showed that increased baseline BSI (hazard ratio [HR], 1.39; 95% confidence interval [CI], 1.04-1.86; P = 0.023) and PSA (HR, 7.15; 95% CI 2.13-24.04; P = 0.0015) values could be independent risk factors for patients with mCRPC without flare. However, these factors lost significance during flare. The risk for all-cause death was significantly higher among patients with BSI > 4 without, than with flare. The results of univariable analyses indicated that flare positively impacted survival (HR, 0.24; 95% CI 0.06‒0.91; P = 0.035). Multivariable analysis did not identify any factors that could predict outcomes.

CONCLUSION

Favorable prognosis, with fewer disturbances from other factors such as the use of abiraterone or/and enzalutamide, PSA changes, and BSI, was attainable in cases when the mCRPC patient demonstrated flare phenomenon. Follow-up bone scintigraphy at least every 3 months could help to determine the prognosis of patients with bone metastasis of mCRPC.

Nuclear medicine imaging for bone metastases assessment: what else besides bone scintigraphy in the era of personalized medicine?

Accurate detection and reliable assessment of therapeutic responses in bone metastases are imperative for guiding treatment decisions, preserving quality of life, and ultimately enhancing overall survival. Nuclear imaging has historically played a pivotal role in this realm, offering a diverse range of radiotracers and imaging modalities. While the conventional bone scan using 99mTc marked bisphosphonates has remained widely utilized, its diagnostic performance is hindered by certain limitations. Positron emission tomography, particularly when coupled with computed tomography, provides improved spatial resolution and diagnostic performance with various pathology-specific radiotracers. This review aims to evaluate the performance of different nuclear imaging modalities in clinical practice for detecting and monitoring the therapeutic responses in bone metastases of diverse origins, addressing their limitations and implications for image interpretation.

Predicting Fractures Using Vertebral 18F-NaF Uptake in Prostate Cancer Patients

BACKGROUND

Patients with prostate cancer tend to be at heightened risk for fracture due to bone metastases and treatment with androgen-deprivation therapy. Bone mineral density (BMD) derived from dual energy X-ray absorptiometry (DXA) is the standard for determining fracture risk in this population. However, BMD often fails to predict many osteoporotic fractures. Patients with prostate cancer also undergo 18F-sodium fluoride (18F-NaF)-positron emission tomography/computed tomography (PET/CT) to monitor metastases. The purpose of this study was to assess whether bone deposition, assessed by 18F-NaF uptake in 18F-NaF PET/CT, could predict incident fractures better than DXA- or CT-derived BMD in patients with prostate cancer.

METHODS

This study included 105 males with prostate cancer who had undergone full body 18F-NaF PET/CT. Standardized uptake value (SUVmean and SUVmax) and CT-derived Hounsfield units (HU), a correlate of BMD, were recorded for each vertebral body. The average SUVmean, SUVmax, and HU were calculated for cervical, thoracic, lumbar, and sacral areas. The t-test was used to assess significant differences between fracture and no-fracture groups.

RESULTS

The SUVmean and SUVmax values for the thoracic area were lower in the fracture group than in the no-fracture group. There was no significant difference in cervical, thoracic, lumbar or sacral HU between the 2 groups.

CONCLUSIONS

Our study reports that lower PET-derived non-metastatic bone deposition in the thoracic spine is correlated with incidence of fractures in patients with prostate cancer. CT-derived HU, a correlate of DXA-derived BMD, was not predictive of fracture risk. 18F-NaF PET/CT may provide important insight into bone quality and fracture risk.

Pseudoprogression after advanced first-line endocrine therapy in metastatic breast cancer with bone metastasis: A case report

Approximately 75% of patients with advanced breast cancer develop bone metastasis, which significantly affects both the quality of life and the survival rate of patients. Accurate determination of the status of bone metastases is important for developing treatment strategies and the prognosis of the disease. Here, we report the case of a 33-year-old patient with advanced metastatic breast cancer (MBC) and multiple bone metastases, in which advanced first-line endocrine therapy and second-line chemotherapy were both considered unsuccessful according to the efficacy evaluation by conventional imaging. Considering the possibility of bone pseudoprogression, the original endocrine scheme was reapplied, and bone metastases achieved a great response of non-complete response (CR)/non-progressive disease (PD). This case showed that, in the course of therapy for the disease, if bone scintigraphy (BS) shows increased lesion density or new lesions, this probably indicates a favorable response (osteoblastic repair of osteolytic lesions) to therapy, and not the worsening of metastatic lesions, called bone pseudoprogression. This paper will provide new insights into strategies for the treatment of bone metastasis and shows the significance of distinguishing osteoblastic bone repair from real bone lesion progression in clinical settings.

Bone and Lymph Node Flare to Androgen Deprivation Therapy in Metastatic Hormone-Sensitive Prostate Cancer on 18F-Prostate-Specific Membrane Antigen PET/CT With Decreasing Prostate-Specific Antigen of 0.7 ng/mL

ABSTRACT

A 72-year-old man with prostate cancer was found to have prostate-specific membrane antigen (PSMA)-avid oligometastasis on initial staging with 18F-DCFPyL PET/CT. Meanwhile, his prostate-specific antigen was 10.0 ng/mL, and testosterone level was 381 ng/dL. Six weeks after initiation of treatment on androgen deprivation therapy plus abiraterone, his restaging 18F-DCFPyL PET/CT showed decreased PSMA uptake in primary prostate lesion, but increased uptake in bone and lymph node metastases, whereas his prostate-specific antigen decreased to 0.7 ng/mL, and testosterone level was <3 ng/dL. This case illustrates hormone-sensitive metastatic bone and lymph node flare on 18F-PSMA PET/CT.

Applications of Artificial Intelligence in 18F-Sodium Fluoride Positron Emission Tomography/Computed Tomography:: Current State and Future Directions

This review discusses the current state of artificial intelligence (AI) in ¹⁸F-NaF-PET/CT imaging and the potential applications to come in diagnosis, prognostication, and improvement of care in patients with bone diseases, with emphasis on the role of AI algorithms in CT bone segmentation, relying on their prevalence in medical imaging and utility in the extraction of spatial information in combined PET/CT studies.

Determination and clinical significance of bone pseudoprogression in hormone receptor-positive metastatic breast cancer

Background

^99mTechnetium labeled methylene diphosphonate bone scans (BSs) are commonly used to monitor disease progression in bone for patients with metastatic breast cancer (MBC). However, new BS lesions may represent osteoblastic bone healing, which we now define as bone pseudoprogression. In this study, we aimed to assess the clinical significance and determination methods of bone pseudoprogression.

Methods

This retrospective analysis was conducted among 48 patients with hormone receptor-positive MBC treated with first-line endocrine therapy. Four months after initiating therapy, all the participants did not show extraosseous disease progression. Participants were divided into two groups according to the presence of new BS lesions. All the patients continued on treatment until explicit disease progression (extraosseous disease progression or progressive lysis on bone lesions). Explicit progression-free survival (PFS) and extraosseous objective response rate were analyzed between the two groups.

Results

New BS lesions were observed in 11 of 48 (22.9%) patients. All the new BS lesions appeared as osteoblastic bone lesions on computed tomography. For patients with new BS lesions, the median PFS was 26.57 months [95% confidence interval (CI) 15.46-37.68], which was similar to that (29.57 months; 95% CI 19.24-39.90) in patients without new BS lesions [hazard ratio: 1.098 (95% CI 0.482-2.503), p = 0.818]. Notably, 82.9% of patients without new BS lesions showed an extraosseous objective response, whereas 85.7% of patients with new BS lesions demonstrated an extraosseous objective response [odds ratio: 0.806 (95% CI 0.061-5.682), p = 0.999]. The median interval between bone pseudoprogression and true disease progression was 21.26 months (95% CI 10.11-32.42).

Conclusions

Osteoblastic new BS lesions detected on follow-up BSs may represent bone pseudoprogression. Clinicians should raise awareness of bone pseudoprogression, thereby avoiding premature discontinuation of therapy and maximizing the opportunity to benefit from endocrine therapy. Due to the small sample size and retrospective nature of the study, large prospective clinical trials are needed to confirm our findings.

Flare phenomenon in prostate cancer: recent evidence on new drugs and next generation imaging

Over the years, an increasing proportion of metastatic prostate cancer patients has been found to experience an initial bone flare phenomenon under both standard therapies (androgen deprivation therapy, chemotherapy, radiotherapy, abiraterone, enzalutamide) and novel agents (immunotherapy, bone-targeting radioisotopes). The underlying biological mechanisms of the flare phenomenon are still elusive and need further clarification, particularly in relation to different types of treatment and their treatment response assessment. Flare phenomenon is often underestimated and, in some cases, can negatively affect clinical outcome. In cases with suspected bone flare, the treatment should be continued for a minimum of 12 more weeks before further decisions about efficacy can be taken. Physicians and patients should be aware of this effect to avoid unwarranted anxiety and inadequate early discontinuation of treatment. This review aims at highlighting new evidence on flare phenomenon arising after the introduction of new drugs extending across the biochemical, radiographic and clinical spectrum of the disease.

Exploring Spatial-Temporal Changes in 18F-Sodium Fluoride PET/CT and Circulating Tumor Cells in Metastatic Castration-Resistant Prostate Cancer Treated With Enzalutamide

PURPOSE

Intrapatient treatment response heterogeneity is under-recognized. Quantitative total bone imaging (QTBI) using ¹⁸F-NaF positron emission tomography/computed tomography (PET/CT) scans is a tool that allows characterization of interlesional treatment response heterogeneity in bone. Understanding spatial-temporal response is important to identify individuals who may benefit from treatment beyond progression.

PATIENTS AND METHODS

Men with progressive metastatic castration-resistant prostate cancer (mCRPC) with at least two lesions on bone scintigraphy were enrolled and treated with enzalutamide 160 mg daily (ClinicalTrials.gov identifier: NCT02384382). ¹⁸F-NaF PET/CT scans were obtained at baseline (PET1), week 13 (PET2), and at the time of prostate-specific antigen (PSA) progression, standard radiographic or clinical progression, or at 2 years without progression (PET3). QTBI was used to determine lesion-level response. The primary end point was the proportion of men with at least one responding bone lesion on PET3 using QTBI.

RESULTS

Twenty-three men were enrolled. Duration on treatment ranged from 1.4 to 34.1 months. In general, global standardized uptake value (SUV) metrics decreased while on enzalutamide (PET2) and increased at the time of progression (PET3). The most robust predictor of PSA progression was change in SUV_hetero (PET1 to PET3; hazard ratio, 3.88; 95% CI, 1.24 to 12.1). Although overall functional disease burden improved during enzalutamide treatment, an increase in total burden (SUV_total) was seen at the time of progression, as measured by ¹⁸F-NaF PET/CT. All (22/22) evaluable men had at least one responding bone lesion at PET3 using QTBI.

CONCLUSION

We found that the proportion of progressing lesions was low, indicating that a substantial number of lesions appear to continue to benefit from enzalutamide beyond progression. Selective targeting of nonresponding lesions may be a reasonable approach to extend benefit.

The changing role of radium-223 in metastatic castrate-resistant prostate cancer: has the EMA missed the mark with revising the label?

Radium-223 (223Ra) is a life-prolonging treatment in symptomatic men with metastatic castrate-resistant prostate cancer (mCRPC) and bone metastases, but no visceral disease, regardless of prior treatment with docetaxel. Together with four other drugs (i.e. abiraterone, cabazitaxel, docetaxel, enzalutamide), it has been available for clinical use since 2013 and has been shown to also provide benefits in quality-of-life and societal benefits. However, in 2018 the European Medicines Agency ruled to restrict the use of radium-223 to a more advanced disease setting after at least two lines of one or the other life-prolonging agent. This decision was triggered by the results of a safety interim analysis of ERA-223, a trial investigating the combination of 223Ra and abiraterone versus abiraterone alone in patients without prior chemotherapy (with the exception of adjuvant treatment) with asymptomatic bone predominant mCRPC. That safety analysis showed an early increased risk of fracture and deaths with the combination treatment. This review critically appraises the available and emerging data with 223Ra treatment in an attempt to assess the appropriateness of the revised label of radium-223.