The significance of equivocal bone findings in staging PSMA imaging in the preoperative setting: validation of the PSMA-RADS version 1.0

Role of cytoreductive radical prostatectomy in men with oligometastatic prostate cancer on molecular imaging

PURPOSE OF REVIEW

The implementation of PET with prostate-specific membrane antigen (PSMA) tracer as primary staging tool occurred recently. Since its introduction, a novel category of patients emerged, with negative staging at conventional imaging, and positive molecular imaging. Local treatment in these patients might be associated with improved oncological outcomes when combined with systemic therapy. However, its impact on oligometastatic prostate cancer (omPCa) remains unknown. In this review, we aimed at investigating the role of cytoreductive radical prostatectomy (cRP) in oligometastatic disease at molecular imaging.

RECENT FINDINGS

After comprehensive review of literature, two retrospective studies highlighted the feasibility, safety, and potential benefits of surgery in omPCA patients at molecular imaging. They showed that 72% of patients achieved PSA less than 0.01 ng/ml following cRP as part of a multimodal approach, 17% experienced radiographic progression, and 7% died at 27-month median follow-up. Moreover, complications postcRP after PSMA PET were modest, with a 40% rate of any adverse event, and 5% of grade more than 3. The 1-year urinary continence after cRP rate was 82%. The oncological, functional outcomes and the complication rate aligned with those observed in series of cRP after conventional imaging.

SUMMARY

cRP is feasible, well tolerated, and effective in selected patients with omPCa at PSMA PET.

Prostate-specific Membrane Antigen Reporting and Data System Version 2.0

Prostate-specific Membrane Antigen Reporting and Data System (PSMA-RADS) was introduced for standardized reporting, and PSMA-RADS version 1.0 allows classification of lesions based on their likelihood of representing a site of prostate cancer on PSMA-targeted positron emission tomography (PET). In recent years, this system has extensively been investigated. Increasing evidence has accumulated that the different categories reflect their actual meanings, such as true positivity in PSMA-RADS 4 and 5 lesions. Interobserver agreement studies demonstrated high concordance among a broad spectrum of 68Ga- or 18F-labeled, PSMA-directed radiotracers, even for less experienced readers. Moreover, this system has also been applied to challenging clinical scenarios and to assist in clinical decision-making, for example, to avoid overtreatment in oligometastatic disease. Nonetheless, with an increasing use of PSMA-RADS 1.0, this framework has shown not only benefits, but also limitations, for example, for follow-up assessment of locally treated lesions. Thus, we aimed to update the PSMA-RADS framework to include a refined set of categories in order to optimize lesion-level characterization and best assist in clinical decision-making (PSMA-RADS version 2.0).

PET Criteria by Cancer Type from Imaging Interpretation to Treatment Response Assessment: Beyond FDG PET Score

Background: in recent years, the role of positron emission tomography (PET) and PET/computed tomography (PET/CT) has emerged as a reliable diagnostic tool in a wide variety of pathological conditions. This review aims to collect and review PET criteria developed for interpretation and treatment response assessment in cases of non-[18F]fluorodeoxyglucose ([18F]FDG) imaging in oncology. Methods: A wide literature search of the PubMed/MEDLINE, Scopus and Google Scholar databases was made to find relevant published articles about non-[18F]FDG PET response criteria. Results: The comprehensive computer literature search revealed 183 articles. On reviewing the titles and abstracts, 149 articles were excluded because the reported data were not within the field of interest. Finally, 34 articles were selected and retrieved in full-text versions. Conclusions: available criteria are a promising tool for the interpretation of non-FDG PET scans, but also to assess the response to therapy and therefore to predict the prognosis. However, oriented clinical trials are needed to clearly evaluate their impact on patient management.

Individual radiosensitivity reflected by γ-H2AX and 53BP1 foci predicts outcome in PSMA-targeted radioligand therapy

PURPOSE

γ-H2AX and 53BP1 are fundamental for cellular DNA damage response (DDR) after radiation exposure and are linked to cell repair, arrest, or apoptosis. We aimed to evaluate whether DDR-markers in peripheral blood lymphocytes (PBLs) may have predictive potential for outcome in metastatic castration-resistant prostate cancer (mCRPC) patients receiving [177Lu]Lu-prostate-specific membrane antigen (PSMA) radioligand therapy (RLT).

METHODS

We prospectively enrolled 20 men with advanced mCRPC scheduled for PSMA-targeted RLT. Prior to the first cycle of [177Lu]Lu-PSMA RLT, all patients underwent [18F]F-PSMA-1007 positron emission tomography (PET)/computed tomography (CT) for assessment of tumor PSMA expression (assessing maximum standardized uptake value (SUVmax) of all tumor lesions). Blood samples were collected prior to, + 1 h after, and + 24 h after administration of [177Lu]Lu-PSMA, and DDR-markers γ-H2AX and 53BP1 were determined in PBLs through immunocytofluorescence. We then tested the predictive performance of DDR-markers relative to clinical and PET-based parameters for progressive disease (PSA-PD) after 2 cycles. In addition, the predictive value for progression-free survival (PSA-PFS, provided as median and 95% confidence interval [CI]) was explored.

RESULTS

Low baseline 53BP1 and γ-H2AX foci (P = 0.17) tended to predict early PSA-PD, whereas low SUVmax was significantly associated with higher risk for PSA-PD (P = 0.04). In Kaplan-Meier analysis, there was a trend towards prolonged PSA-PFS in patients with higher baseline 53BP1 of 6 months (mo; 95%CI, 4-9 mo) compared to 3 mo in patients with low 53BP1 (95% CI, 2-3 mo; P = 0.12). Comparable results were recorded for higher γ-H2AX expression (6 mo [95% CI, 3-9 mo] relative to 3 mo [95% CI, 2-4 mo] in patients with low γ-H2AX; P = 0.12). SUVmax, however, did not demonstrate predictive value (P = 0.29). Consistently, in univariate Cox-regression analysis, baseline 53BP1 foci demonstrated borderline significance for predicting PSA-PFS under [177Lu]Lu-PSMA RLT (P = 0.05).

CONCLUSION

In this prospective study investigating mCRPC patients undergoing [177Lu]Lu-PSMA RLT, low baseline DDR-markers in PBLs tended to predict poor outcome. Although the study group was small and results need further confirmation, these preliminary findings lay the foundation for exploring additive radiosensitizing or treatment intensification in future studies with high-risk individuals scheduled for RLT.

Bone Uptake in Prostate Cancer Patients: Diagnostic Performances of PSMA-RADS v1.0, Clinical, Biological, and 68 Ga-PSMA-11 PET Features to Predict Metastasis After Biochemical Recurrence

PURPOSE

68 Gallium-labeled prostate-specific membrane antigen-11 (PSMA) PET/CT is the new reference to identify relapse during biochemical recurrence of prostate cancer (PCa). However, this method lacks specificity for bone foci. This study aimed to report the prevalence of PCa bone metastases and to assess the diagnostic performances of PSMA reporting and data systems (RADS), clinical, biological, and imaging features for identification.

PATIENTS AND METHODS

A multicentric retrospective cohort of consecutive patients with biochemical recurrence after local treatment was analyzed. Clinical and biological features at initial staging and during recurrence were retrieved from medical reports. The metastatic status of each bone uptake on PSMA PET/CT was determined according to histopathology, comparisons with concomitant and previous conventional imaging, prostate-specific antigen kinetic, and follow-up. Two nuclear medicine physicians assessed PSMA-RADS, anatomic location, radiological patterns, SUV max , and the presence of other molecular lesions. Univariate and multivariate analyses were conducted to identify independent predictors of PCa metastases.

RESULTS

In the eligible population, 98/298 patients (32.9%) showed bone uptake on PSMA PET/CT. In patients with a final diagnosis, 28/81 lesions (34.6%) were metastases. PSMA-RADS-4 or 5 showed sensitivity of 79%, specificity of 94%, and accuracy of 89%. PSMA-RADS had a significantly higher area under the receiver operating characteristic curve than the initial reading in clinical practice (0.91 vs 0.83, P = 0.0074). Initial Gleason score ≥8, age ≤71 years at recurrence, and SUV max >6.21 were independent predictors of PCa metastases in multivariate logistic regression ( P = 0.0314, 0.0179, and 0.0003, respectively).

CONCLUSIONS

Most bone uptakes at PSMA PET/CT were benign lesions. PSMA-RADS, patients and tumor characteristics, and SUV max could help identify PCa bone metastases.

Indeterminate skeletal and lymph node lesion on 18F PSMA 1007 PET/CT scanning: lessons from a review at 12 months with PSMA-RADS

AIMS OF THE STUDY

The study utilizes the prostate-specific membrane antigen-reporting and data system (PSMA-RADS) version 1.0 in a real-world patient scenario in the evaluation of equivocal lesions using the PSMA-RADS categorization for patient management and communication in multidisciplinary team (MDT) meetings.

METHODS

A retrospective analysis of 203 patients who had 18F PSMA PET/CT for either restaging or staging over 12 months was undertaken. The scans were evaluated for local disease, lymph node involvement and distant metastases. The scan findings were classified as suspicious for metastases, and equivocal and benign lesions. Experience with PSMA ligand imaging was considered while classifying the lesions, equivocal lesions were assessed with PSMA-RADS and followed up with complementary imaging and/or clinical follow-up assessment or MDT for further patient management.

RESULTS

A total of 91 of 203 patients had equivocal lesions. Follow-up assessment was performed in 47 of 91 patients with imaging (n = 36) or MDT discussion (n = 11).On follow-up imaging (n = 36), equivocal lesion was seen in skeletal lesions (n = 24), pelvic lymph nodes (n = 6), both skeletal and pelvic nodes (n = 4), hilar and mediastinal lymph nodes (n = 1) and spleen (n = 1). The patients were reclassified as benign, metastatic with few lesion remained equivocal. Overall follow-up assessment impacted clinical management in 47% patients.

CONCLUSION

18F PSMA PET/CT may show equivocal lesions; many of them in the skeleton, a small proportion of which are ultimately proven metastatic. In contrast, a higher proportion of the equivocal nodes in the pelvis end up being metastatic on follow-up. A structured reporting with PSMA-RADS grading helps in the proper classification of lesions and standardization of reports.

Assessment of malignancy and PSMA expression of uncertain bone foci in [18F]PSMA-1007 PET/CT for prostate cancer-a single-centre experience of PET-guided biopsies

Purpose

Uncertain focal bone uptake (UBU) with intensive radiopharmaceutical avidity are frequently observed in patients undergoing [¹⁸F]PSMA-1007 PET/CT for the detection of prostate cancer (PC). Such foci can pose diagnostic conundrums and risk incorrect staging. The aim of this short communication is to share the results of PET-guided biopsies of such foci.

Methods

A retrospective analysis revealed 10 patients who were referred to our department for PET-guided biopsy of UBU visible in a previous [¹⁸F]PSMA-1007 PET/CT. [¹⁸F]-PSMA-1007 PET-guided biopsy was conducted for 11 PSMA-avid bone foci in these 10 patients. The biopsy materials were analysed for tissue typing, and immunohistochemistry (IHC) was performed for prostate-specific-membrane-antigen (PSMA) expression. The scans were analysed by two experienced physicians in a consensus read for clinical characteristics and radiopharmaceutical uptake of foci.

Results

One out of 11 (9.1%) of the foci biopsied was confirmed as bone metastasis of PC with intense PSMA-expression, while 10/11 (90.9%) foci were revealed to be unremarkable bone tissue without evidence of PSMA expression at IHC. Amongst all bone foci assessed by biopsy, eight were visually classified as being at high risk of malignancy in the PET/CT (SUVmean 12.0 ± 8.1; SUVmax 18.8 ± 13.1), three as equivocal (SUVmean 4.6 ± 2.1; SUVmax 7.2 ± 3.0) and zero as low risk. No UBU had any CT correlate.

Conclusions

This cohort biopsy revealed that a small but relevant number of UBU are true metastases. For those confirmed as benign, no PSMA expression at IHC was observed, suggesting a non-PSMA mediated cause for intensive [¹⁸F]PSMA-1007 uptake of which the reason remains unclear. Readers must interpret such foci with caution in order to reduce the risk of erroneous staging and subsequent treatment. PET-guided biopsy, particularly in the absence of morphological changes in the CT, can be a useful method to clarify such foci.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05745-5.

Freely available artificial intelligence for pelvic lymph node metastases in PSMA PET-CT that performs on par with nuclear medicine physicians

PURPOSE

The aim of this study was to develop and validate an artificial intelligence (AI)-based method using convolutional neural networks (CNNs) for the detection of pelvic lymph node metastases in scans obtained using [¹⁸F]PSMA-1007 positron emission tomography-computed tomography (PET-CT) from patients with high-risk prostate cancer. The second goal was to make the AI-based method available to other researchers.

METHODS

[¹⁸F]PSMA PET-CT scans were collected from 211 patients. Suspected pelvic lymph node metastases were marked by three independent readers. A CNN was developed and trained on a training and validation group of 161 of the patients. The performance of the AI method and the inter-observer agreement between the three readers were assessed in a separate test group of 50 patients.

RESULTS

The sensitivity of the AI method for detecting pelvic lymph node metastases was 82%, and the corresponding sensitivity for the human readers was 77% on average. The average number of false positives was 1.8 per patient. A total of 5-17 false negative lesions in the whole cohort were found, depending on which reader was used as a reference. The method is available for researchers at www.recomia.org .

CONCLUSION

This study shows that AI can obtain a sensitivity on par with that of physicians with a reasonable number of false positives. The difficulty in achieving high inter-observer sensitivity emphasizes the need for automated methods. On the road to qualifying AI tools for clinical use, independent validation is critical and allows performance to be assessed in studies from different hospitals. Therefore, we have made our AI tool freely available to other researchers.

Staging 68 Ga-PSMA PET/CT in 963 consecutive patients with newly diagnosed prostate cancer: incidence and characterization of skeletal involvement

PURPOSE

The aim of the study was to elaborate the incidence and type of skeletal involvement in a large cohort of patients with newly diagnosed prostate cancer (PCa) referred for Ga-68 PSMA-11 PET/CT staging in a single center.

METHODS

Study cohort included 963 consecutive patients with newly diagnosed PCa referred for Ga-68 PSMA-11 PET/CT study for staging. The incidence of bone involvement, type of bone metastases, and extent of disease were determined and correlated with the ISUP Grade Group (GG) criteria and PSA levels.

RESULTS

Bone metastases were found in 188 (19.5%) of 963 patients. Bone metastases were found in 10.7% of patients with PSA < 10 ng/dL and in 27.4% of patients with PSA > 10 ng/dL and in 6.1% of patients with GG ≤ 2/3 and in 8.9% of patients with GG 4/5. In 7.6% of the patients, skeletal involvement was extensive, while 11.9% of patients had oligometastatic disease. Osteoblastic type metastases were the most common type of bone metastases presented in 133 of the patients with malignant bone involvement (70.7%). More than half of them had only osteoblastic lesions (72 patients (38.3%)), while the other (61 patients (32.5%)) had also intramedullary and/or osteolytic type lesions. Intramedullary metastases were found in 97 patients (51.6%), while 41 (21.8%) of them were only intramedullary lesions. Osteolytic metastases were detected in 36 patients (19.2%), of which 8 were only osteolytic lesions.

CONCLUSION

Although traditionally bone metastases of PCa are considered osteoblastic, osteolytic and intramedullary metastases are common, as identified on PET with labeled PSMA. Skeletal spread may be present also in patients with GG ≤ 2/3 and PSA < 10 ng/dL.

Clinical insignificance of [18F]PSMA-1007 avid non-specific bone lesions: a retrospective evaluation

PURPOSE

[18F]PSMA-1007 offers advantages of low urinary tracer excretion and theoretical improved spatial resolution for imaging prostate cancer. However, non-specific bone lesions (NSBLs), defined as mild to moderate focal bone uptake without a typical morphological correlate on CT, are a common finding on [18F]PSMA-1007 PET/CT. The purpose of this study was to investigate the clinical outcomes of patients with [18F]PSMA-1007 avid NSBLs, to determine whether patients with NSBLs represent a higher risk clinical cohort, and to determine whether SUVmax can be used as a classifier of bone metastasis.

METHODS

A retrospective audit of 214 men with prostate cancer was performed to investigate the clinical outcomes of [18F]PSMA-1007 avid NSBLs according to defined criteria. We also compared the serum PSA, Gleason score, and uptake time of patients with [18F]PSMA-1007 avid NSBLs to patients without [18F]PSMA-1007 avid bone lesions. Finally, we analysed an SUVmax threshold to identify bone metastases using ROC curve analysis.

RESULTS

Ninety-four of 214 patients (43.9%) demonstrated at least one NSBL. No [18F]PSMA-1007 avid NSBLs met criteria for a likely malignant or definitely malignant lesion after a median 15.8-month follow-up interval (11.9% definitely benign, 50.3% likely benign, and 37.7% equivocal). There were no statistically significant differences in serum PSA, Gleason score, and uptake time between patients with [18F]PSMA-1007 avid NSBLs and those without [18F]PSMA-1007 avid bone lesions. All NSBLs with adequate follow-up had SUVmax ≤ 11.1. The value of the highest SUVmax distinguished between NSBLs and definite prostate cancer bone metastases, whereby an SUVmax threshold of ≥ 7.2 maximized the Youden's index.

CONCLUSION

[18F]PSMA-1007 avid NSBLs rarely represent prostate cancer bone metastases. When identified in the absence of definite metastatic disease elsewhere, it is appropriate to classify those with SUVmax < 7.2 as likely benign. NSBLs with SUVmax 7.2-11.1 may be classified as equivocal or metastatic, with patient clinical risk factors, scan appearance, and potential management implications used to guide interpretation.

Comparing the clinical performance and cost efficacy of [68Ga]Ga-PSMA-11 and [18F]PSMA-1007 in the diagnosis of recurrent prostate cancer: a Markov chain decision analysis

Purpose

Amongst others, [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]PSMA-1007 are available for the detection of recurrent prostate cancer (rPC). There are currently limited data comparing the performance of these two radioligands with respect to clinical outcomes or their cost efficacy, which this study aims to address.

Methods

Two hundred and forty-four patients undergoing PSMA PET/CT for rPC were retrospectively analysed for this study (one hundred and twenty two with each radiopharmaceutical) to generate rates of PET positivity, negativity and unclear findings. Patients underwent follow-up to determine the rate of additional examinations and to confirm PET findings. A Markov chain decision analysis was implemented to model clinical decision-making processes and to analyse clinical performance of the two tracers. We determine their clinical cost efficacies using cost data from several countries where both radiotracers are in routine use.

Results

The PET positivity rate was non-significantly higher for [¹⁸F]PSMA-1007 compared to [⁶⁸Ga]Ga-PSMA-11 (91.8% vs. 86.9%, p = 0.68), whereas the rate of uncertain findings was significantly greater (17.2% vs. 8.25%, p = 0.02). The probability of a true positive finding was higher for [⁶⁸Ga]Ga-PSMA-11 (0.90, 95% CI 0.70-0.98) vs. [¹⁸F]PSMA-1007 (0.81, 95% CI 0.66–0.91). A significantly (p < 0.0001) higher PPV for [⁶⁸Ga]Ga-PSMA-11 (0.99, 95% CI 0.99–1.0 vs. 0.86) was found compared to [¹⁸F]PSMA-1007 (0.86, 95% CI 0.82–1.00). Intervention efficacy analysis favoured [⁶⁸Ga]Ga-PSMA-11, where the number needed to image (to achieve a true positive finding) was 10.58 and the number needed to image to harm (to achieve a false positive finding) was − 8.08. A cost efficacy analysis favours [⁶⁸Ga]Ga-PSMA-11 in three of the four jurisdictions analysed where health economic data was available (Switzerland, Israel, Australia) and [¹⁸F]PSMA-1007 in one jurisdiction (Denmark).

Conclusion

The analysis reveals a non-significantly higher PET positivity rate for [¹⁸F]PSMA-1007, but finds significantly greater rates of uncertain findings and false positive findings when compared to [⁶⁸Ga]Ga-PSMA-11. We find differences in the two tracers in terms of clinical performance and cost efficacy. The method presented herein is generalisable and can be used with clinical or cost data for other countries or tracers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05620-9.

Intraindividual comparison of [68 Ga]-Ga-PSMA-11 and [18F]-F-PSMA-1007 in prostate cancer patients: a retrospective single-center analysis

BACKGROUND

The analysis aimed to compare the radiotracers [⁶⁸Ga]-Ga-PSMA-11 and [¹⁸F]-F-PSMA-1007 intraindividually in terms of malignant lesions, mi(molecular-imaging)TNM staging and presumable unspecific lesions retrospectively as used in routine clinical practice.

METHODS

A retrospective analysis of 46 prostate cancer patients (median age: 71 years) who underwent consecutive [⁶⁸Ga]-Ga-PSMA-11- and [¹⁸F]-F-PSMA-1007-PET/CT or PET/MRI within a mean of 12 ± 8.0 days was performed. MiTNM staging was performed in both studies by two nuclear medicine physicians who were blinded to the results of the other tracer. After intradisciplinary and interdisciplinary consensus with two radiologists was reached, differences in both malignant and presumable nonspecific tracer accumulation were analyzed.

RESULTS

Differences in terms of miTNM stages in both studies occurred in nine of the 46 patients (19.6%). The miT stages differed in five patients (10.9%), the miN stages differed in three patients (6.5%), and different miM stages occurred only in one patient who was upstaged in [¹⁸F]-F-PSMA-1007 PET. Concordant miTNM stages were obtained in 37 patients (80.4%). There was no significant difference between [¹⁸F]-F-PSMA-1007 and [⁶⁸Ga]-Ga-PSMA-11 in the SUV_max locally (31.5 vs. 32.7; p = 0.658), in lymph node metastases (28.9 vs. 24.9; p = 0.30) or in bone metastases (22.9 vs. 27.6; p = 0.286). In [¹⁸F]-F-PSMA-1007 PET, more patients featured presumable unspecific uptake in the lymph nodes (52.2% vs. 28.3%; p: < 0.001), bones (71.7% vs. 23.9%; p < 0.001) and ganglia (71.7% vs. 43.5%; p < 0.001). Probable unspecific, exclusively [¹⁸F]-F-PSMA-1007-positive lesions mainly occurred in the ribs (58.7%), axillary lymph nodes (39.1%) and cervical ganglia (28.3%).

CONCLUSION

In terms of miTNM staging, both tracers appeared widely exchangeable, as no tracer relevantly outperformed the other. The differences between the two tracers were far more common in presumable unspecific lesions than in malignant spots. A routinely performed two-tracer study could not be shown to be superior. Since it seems at least challenging for most nuclear medicine departments to provide both [¹⁸F]-F-PSMA-1007 and [⁶⁸Ga]-Ga-PSMA-11, it appears reasonable to choose the PSMA radiotracer depending on local availability with attention to the greater occurrence of nonspecific bone findings with [¹⁸F]-F-PSMA-1007.