Characterization of indeterminate renal masses with molecular imaging: how do we turn potential into reality?

Lack of effect of renal function on uptake of 99m Tc-sestamibi in renal masses

OBJECTIVE

The appropriate clinical management of indeterminate small renal masses can be improved based on accurate risk stratification. This study aimed to investigate the impact of renal function on the uptake of technetium-99m ( 99m Tc)-sestamibi, a widely available imaging agent that can be utilized to identify oncocytomas and other benign/indolent renal masses.

METHODS

A retrospective cohort study was conducted, involving 100 consecutive patients who underwent 99m Tc-sestamibi single-photon emission computed tomography/computed tomography. Renal function was evaluated based on creatinine levels and glomerular filtration rate (GFR). Statistical analyses, including correlation and regression analyses, were performed to explore the relationship between renal function and 99m Tc-sestamibi uptake.

RESULTS

The results revealed that discrepancies can occur between imaging and pathology results, emphasizing the need for careful interpretation of imaging findings. Correlation analysis demonstrated no significant correlation between relative tumor uptake of 99m Tc-sestamibi and GFR or serum creatinine levels. These findings highlight the relative independence of renal function and 99m Tc-sestamibi uptake and suggest sestamibi may be of use even in patients with relatively poor renal function.

CONCLUSIONS

However, further research with larger sample sizes is required to validate and generalize these findings. Ultimately, understanding the broad variety of applicability of 99m Tc-sestamibi uptake for risk stratification of renal malignancy could aid in appropriate clinical decision-making.

Molecular imaging for non-invasive risk stratification of renal masses

Anatomic imaging with contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) has long been the mainstay of renal mass characterization. However, those modalities are often unable to adequately characterize indeterminate, solid, enhancing renal masses - with some exceptions, such as the development of the clear-cell likelihood score on multi-parametric MRI. As such, molecular imaging approaches have gained traction as an alternative to anatomic imaging. Mitochondrial imaging with 99mTc-sestamibi single-photon emission computed tomography/CT is a cost-effective means of non-invasively identifying oncocytomas and other indolent renal masses. On the other end of the spectrum, carbonic anhydrase IX agents, most notably the monoclonal antibody girentuximab - which can be labeled with positron emission tomography radionuclides such as zirconium-89 - are effective at identifying renal masses that are likely to be aggressive clear cell renal cell carcinomas. Renal mass biopsy, which has a relatively high non-diagnostic rate and does not definitively characterize many oncocytic neoplasms, nonetheless may play an important role in any algorithm targeted to renal mass risk stratification. The combination of molecular imaging and biopsy in selected patients with other advanced imaging methods, such as artificial intelligence/machine learning and the abstraction of radiomics features, offers the optimal way forward for maximization of the information to be gained from risk stratification of indeterminate renal masses. With the proper application of those methods, inappropriately aggressive therapy for benign and indolent renal masses may be curtailed.

PET/Computed Tomography Transformation of Oncology: Kidney and Urinary Tract Cancers

Renal cell carcinoma (RCC) and urothelial carcinoma (UC) are two of the most common genitourinary malignancies. 2-deoxy-2-[18F]fluoro-d-glucose (18F-FDG) can play an important role in the evaluation of patients with RCC and UC. In addition to the clinical utility of 18F-FDG PET to evaluate for metastatic RCC or UC, the shift in molecular imaging to focus on specific ligand-receptor interactions should provide novel diagnostic and therapeutic opportunities in genitourinary malignancies. In combination with the rise of artificial intelligence, our ability to derive imaging biomarkers that are associated with treatment selection, response assessment, and overall patient prognostication will only improve.

Predicting conversion of brain β-amyloid positivity in amyloid-negative individuals

Background

Cortical deposition of β-amyloid (Aβ) plaque is one of the main hallmarks of Alzheimer’s disease (AD). While Aβ positivity has been the main concern so far, predicting whether Aβ (−) individuals will convert to Aβ (+) has become crucial in clinical and research aspects. In this study, we aimed to develop a classifier that predicts the conversion from Aβ (−) to Aβ (+) using artificial intelligence.

Methods

Data were obtained from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort regarding patients who were initially Aβ (−). We developed an artificial neural network-based classifier with baseline age, gender, APOE ε4 genotype, and global and regional standardized uptake value ratios (SUVRs) from positron emission tomography. Ten times repeated 10-fold cross-validation was performed for model measurement, and the feature importance was assessed. To validate the prediction model, we recruited subjects at the Samsung Medical Center (SMC).

Results

A total of 229 participants (53 converters) from the ADNI dataset and a total of 40 subjects (10 converters) from the SMC dataset were included. The average area under the receiver operating characteristic values of three developed models are as follows: Model 1 (age, gender, APOE ε4) of 0.674, Model 2 (age, gender, APOE ε4, global SUVR) of 0.814, and Model 3 (age, gender, APOE ε4, global and regional SUVR) of 0.841. External validation result showed an AUROC of 0.900.

Conclusion

We developed prediction models regarding Aβ positivity conversion. With the growing recognition of the need for earlier intervention in AD, the results of this study are expected to contribute to the screening of early treatment candidates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01067-8.

In Situ Metabolomics Expands the Spectrum of Renal Tumours Positive on 99mTc-sestamibi Single Photon Emission Computed Tomography/Computed Tomography Examination

Background

Definite noninvasive characterisation of renal tumours positive on ^99mTc-sestamibi single photon emission computed tomography/computed tomography (SPECT/CT) examination including renal oncocytomas (ROs), hybrid oncocytic chromophobe tumours (HOCTs), and chromophobe renal cell carcinoma (chRCC) is currently not feasible.

Objective

To investigate whether combined ^99mTc-sestamibi SPECT/CT and in situ metabolomic profiling can accurately characterise renal tumours exhibiting ^99mTc-sestamibi uptake.

Design, setting, and participants

A tissue microarray analysis of 33 tumour samples from 28 patients was used to investigate whether their in situ metabolomic status correlates with their features on ^99mTc-sestamibi SPECT/CT examination. In order to validate emerging data, an independent cohort comprising 117 tumours was subjected to matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI MSI).

Outcome measurements and statistical analysis

MALDI MSI data analysis and image generation were facilitated by FlexImaging v. 4.2, while k-means analysis by SCiLS Lab software followed by R-package CARRoT analysis was used for assessing the highest predictive power in the differential of RO versus chRCC. Heatmap-based clustering, sparse partial least-squares discriminant analysis, and volcano plots were created with MetaboAnalyst 3.0.

Results and limitations

We identified a discriminatory metabolomic signature for ^99mTc-sestamibi SPECT/CT–positive Birt-Hogg-Dubè–associated HOCTs versus other renal oncocytic tumours. Metabolomic differences were also evident between ^99mTc-sestamibi–positive and ^99mTc-sestamibi–negative chRCCs, prompting additional expert review; two of three ^99mTc-sestamibi–positive chRCCs were reclassified as low-grade oncocytic tumours (LOTs). Differences were identified between distal-derived tumours from those of proximal tubule origin, including differences between ROs and chRCCs.

Conclusions

The current study expands the spectrum of ^99mTc-sestamibi SPECT/CT–positive renal tumours, encompassing ROs, HOCTs, LOTs, and chRCCs, and supports the feasibility of in situ metabolomic profiling in the diagnostics and classification of renal tumours.

Patient summary

For preoperative evaluation of solid renal tumours, ^99mTc-sestamibi single photon emission computed tomography/computed tomography (SPECT/CT) is a novel examination method. To increase diagnostic accuracy, we propose that ^99mTc-sestamibi–positive renal tumours should be biopsied and followed by a combined histometabolomic analysis.

Reporting and handling of equivocal imaging findings in diagnostic studies of bone metastasis in prostate cancer

BACKGROUND

Equivocal scanning results occur. It remains unclear how these results are presented and their management influence diagnostic characteristics.

PURPOSE

To investigate the reporting and handling of equivocal imaging findings in diagnostic studies of bone metastases, and to assess the impact on diagnostic performance of the methods used to analyze equivocal findings. The conceptual issue was reified based on two actual observations.

MATERIAL AND METHODS

A recent meta-analysis of bone metastases in prostate cancer was conducted and data were obtained from a large clinical trial with a true reference of bone metastasis, where diagnostic characteristics were calculated with equivocal scans handled by: removal; considered malignant; considered benign; and intention-to-diagnose.

RESULTS

The meta-analysis included 18 trials where the median proportion of reported equivocal results was 27%. Eleven (61%) studies reported an equivocal option for the index test, 42% reported equivocal results and described how these were analyzed. The clinical trial included 583 prostate cancer patients with 20% equivocal results. The different methods of managing equivocal findings resulted in highly variable outcomes: sensitivity = 85%-100%; specificity = 78%-99%; and positive and negative predictive values = 44%-94% and 97%-100%, respectively. The diagnostic performances obtained using the four methods were differentially susceptible to the proportion of equivocal imaging findings and the prevalence of bone metastases.

CONCLUSION

Reporting of equivocal results was inadequate in bone imaging trials. The handling of equivocal findings strongly influenced diagnostic accuracy.

Diagnostic accuracy of 99mTc-sestamibi SPECT/CT for detecting renal oncocytomas and other benign renal lesions: a systematic review and meta-analysis

PURPOSE

The primary objectives of this systematic review and meta-analysis were to evaluate the diagnostic accuracy of 99mTc-sestamibi SPECT/CT for detecting renal oncocytoma versus (1) all other renal lesions and (2) chromophobe renal cell carcinoma (ChrRCC) alone.

METHODS

A systematic review of MEDLINE, EMBASE, Scopus, the Cochrane Library, and the Gray Literature was performed. Original articles with > 5 patients evaluating oncocytomas versus other renal lesions with SPECT/CT using a pathological reference standard were included. Patient, clinical, imaging, and performance parameters were independently acquired by two reviewers. Meta-analysis was performed using a bivariate mixed-effects regression model.

RESULTS

Four articles with a total of 117 renal lesions were included in analysis. The pooled and weighted sensitivity and specificity values of 99mTc-sestamibi SPECT/CT for detecting (1) renal oncocytoma versus other renal lesions were 92% (95% CI 72-98%) and 88% (95% CI 79-94%), respectively, and (2) 89% and 67%, respectively, for renal oncocytoma versus ChrRCC. The specificity for the detecting the oncocytoma-ChrRCC spectrum was 96% (95% CI 84-99%). The sensitivity and specificity for detecting benign versus malignant renal lesions were 86% (95% CI 66-95%) and 90% (95% CI 80-95%), and 88% and 95% when HOCTs were characterized as benign. All reporting studies used a cut-off tumor-to-background renal parenchyma radiotracer uptake ratio of > 0.6 for positive studies.

CONCLUSION

99mTc-sestamibi SPECT/CT demonstrates a high sensitivity and specificity for characterizing benign and low-grade renal lesions. This test can help improve the diagnostic confidence for patients with indeterminate renal masses being considered for active surveillance.

Utilization and Operative Influence of Renal Mass Biopsy in the Small Renal Mass: Analysis from the Clinical Research Office of the Endourological Society Small Renal Mass registry

Introduction and Objective: Definitive inclusion of renal mass biopsy (RMB) in small renal mass (SRM) diagnostic algorithm remains controversial. We assessed incidence and accuracy of RMB in SRMs in the CROES Renal Mass registry and the influence of preoperative RMB on perioperative complications after SRM nephron-sparing surgery (NSS). Materials and Methods: "ad hoc" description of incidence of preoperative RMB and characteristics of SRM cases with and without RMB. Accuracy of RMB was calculated in the SRM subcohort that received extirpative treatment and complication rate after NSS compared to between the two groups. Continuous variables were compared using t-test; categorical variables were compared using the chi-square test. K-statistics was used to analyze agreement between the biopsy histology and surgical pathology. Logistic regression was used to assess the association between RMB and NSS complications. All tests were two sided, and p-values <0.05 were considered statistically significant. Results: The rate of preoperative RMB in SRMs was 11.6% (175/1597) in Europe and the United States. RMB patients were more likely to have hypertension (p < 0.04), be on dialysis (p < 0.024), or smokers (p = 0.005), with multiple/bilateral tumors (0.008 and 0.010) and previous other malignancy (p = 0.021). They underwent radical nephrectomy more frequently than non-RMB group (p = 0.034). RMB was nondiagnostic in 16 cases (9%). Accuracy of RMB in distinguishing malignant from benign was 89.5%. Agreement between biopsy and final surgical pathology was 93% for malignant vs benign tumors (kappa = 0.655). Upstaging to pT3a occurred more frequently in the RMB group (12.6% vs 6.25% [p = 0.022]). Complication rate in renal mass-NSS subcohort was 15.8%, not statistically different between RMB and non-RMB groups. On logistic regression analysis, RMB was not associated with increased risk of postoperative complication after NSS (OR: 0.9, 95% CI: 0.43-1.89). Conclusion: The practice of RMB in SRM is still scarce despite high accuracy and concordance with final pathology. RMB does not seem to increase complication rate after NSS.

3D CT of renal pathology: initial experience with cinematic rendering

3D computed tomography (CT) visualizations of volumetric data have become an important aspect of diagnostic imaging. The utility of 3D CT has been well described for the imaging of a number of renal pathologies. Recently, a new 3D visualization technique known as cinematic rendering (CR) has become available and provides photorealistic images derived from standard CT acquisitions by use of a complex global lighting model. Herein, we describe a number of normal variant and pathologic conditions of the kidney visualized with CR. We provide comparisons of findings with CR to traditional methods of 3D imaging and comment on the potential applications of this new method of 3D CT rendering.

Reporting and Handling of Indeterminate Bone Scan Results in the Staging of Prostate Cancer: A Systematic Review

Bone scintigraphy is key in imaging skeletal metastases in newly diagnosed prostate cancer. Unfortunately, a notable proportion of scans are not readily classified as positive or negative but deemed indeterminate. The extent of reporting of indeterminate bone scans and how such scans are handled in clinical trials are not known. A systematic review was conducted using electronic databases up to October 2016. The main outcome of interest was the reporting of indeterminate bone scans, analyses of how such scans were managed, and exploratory analyses of the association of study characteristics and the reporting of indeterminate bone scan results. Seventy-four eligible clinical trials were identified. The trials were mostly retrospective (85%), observational (95%), large trials (median 195 patients) from five continents published over four decades. The majority of studies had university affiliation (72%), and an author with imaging background (685). Forty-five studies (61%) reported an indeterminate option for the bone scan and 23 studies reported the proportion of indeterminate scans (median 11.4%). Most trials (44/45, 98%) reported how to handle indeterminate scans. Most trials (n = 39) used add-on supplementary imaging, follow-up bone scans, or both. Exploratory analyses showed a significant association of reporting of indeterminate results and number of patients in the study (p = 0.024) but failed to reach statistical significance with other variables tested. Indeterminate bone scan for staging of prostate cancer was insufficiently reported in clinical trials. In the case of indeterminate scans, most studies provided adequate measures to obtain the final status of the patients.

Correlation of 99mTc-sestamibi uptake in renal masses with mitochondrial content and multi-drug resistance pump expression

Background

^99mTc-sestamibi single-photon emission computed tomography/computed tomography (SPECT/CT) has recently been explored for the characterization of indeterminate renal masses. As judged by increased intra-tumoral radiotracer uptake, we have previously reported the excellent diagnostic performance characteristics of this test for identifying benign/indolent oncocytomas and hybrid oncocytic/chromophobe tumors (HOCTs). In this study, we investigated potential molecular mechanisms underlying the discriminatory ability of ^99mTc-sestamibi SPECT/CT for renal masses.

Fifty renal masses imaged with ^99mTc-sestamibi SPECT/CT prior to surgical resection were evaluated by immunohistochemistry for mitochondrial content and expression of the multi-drug resistance pump 1 (MDR1/P-gp). Immunohistochemical staining was scored semi-quantitatively, and results were compared across renal tumor histologies and correlated with ^99mTc-sestamibi uptake.

Results

In total, 6/6 (100%) and 2/2 (100%) HOCTs demonstrated strong mitochondrial content staining combined with low MDR1 staining. Clear cell renal cell carcinoma showed an opposite pattern with the majority having low mitochondrial (14/26, 54%) and high MDR1 staining (18/26, 69%). Other tumor types were more variable in staining pattern, although the staining pattern reliably predicted ^99mTc-sestamibi uptake in almost all tumors except chromophobe renal cell carcinoma.

Conclusions

Our findings confirm that renal tumors with high mitochondrial content and relatively low MDR pump expression activity accumulate ^99mTc-sestamibi and allow for the accurate diagnosis of the benign/indolent tumor class that includes oncocytomas and HOCTs. For masses in which MDR activity outweighs the presence of mitochondria, the tumors appear cold on ^99mTc-sestamibi SPECT/CT, allowing for high confidence in the diagnosis of renal cell carcinoma.