Opportunities and challenges for MRD assessment in the clinical management of multiple myeloma

Measurable residual disease (MRD) assessment is, from the methodological point of view, ready for prime time in multiple myeloma (MM). Abundant evidence underscores the value of MRD status determined using highly sensitive next-generation flow cytometry and next-generation sequencing tests in evaluating response to treatment and, therefore, prognosis in patients with this disease. MRD response assessment and monitoring might present a range of opportunities for individualized patient management. Moreover, the considerable amounts of high-quality and standardized MRD data generated in clinical trials have led to the acceptance of MRD negativity as an early end point for accelerated regulatory approval of treatments for MM. The data leave no doubt that the efficacy of new regimens in inducing deeper and durable MRD-negative responses is connected with prolonged survival. Yet, several evidential, technical and practical challenges continue to limit the implementation of MRD-guided treatment strategies in routine practice, and the use of MRD as a surrogate end point remains controversial to some. In this Review, we draw on past and present research to propose opportunities for overcoming some of these challenges, and to accelerate the use of MRD assessment for improved clinical management of patients with MM.

Are we maintaining minimal residual disease in myeloma?

Minimal residual disease (MRD) has emerged as an important prognostic maker in patients with multiple myeloma at different stages of their treatment. Moreover, it is being increasingly incorporated as an endpoint in various clinical trials. Since maintenance therapy is an integral part of myeloma treatment, especially in the upfront setting post autologous transplantation, it is imperative to understand the role of MRD testing in the maintenance stetting. This review aims to examine the utility and dynamics of MRD testing in order to elucidate its prognostic role and possible incorporation in clinical decision making processes.

68 Ga-Pentixafor PET/CT-Based Response Evaluation and its Prognostic Value in Multiple Myeloma: Comparison With IMWG and 18 F-FDG-Based Response

PURPOSE

68 Ga-Pentixafor PET/CT targets CXCR4 receptors and provides superior diagnostic accuracy in multiple myeloma (MM) compared with 18 F-FDG PET/CT. However, its role in response evaluation remains unexplored. We propose a 68 Ga-Pentixafor PET/CT-based response evaluation criterion and evaluate its utility compared with International Myeloma Working Group (IMWG) criteria and 18 F-FDG PET/CT-based response.

PATIENTS AND METHODS

In this prospective single-center study, 40 treatment-naive myeloma patients were recruited between February 2021 and April 2023. Both 68 Ga-Pentixafor and 18 F-FDG PET/CT were performed at baseline and at follow-up (7.2 mo-median). Response to treatment was evaluated using the proposed 68 Ga-Pentixafor PET/CT criteria and compared with responses assessed by IMWG and 18 F-FDG PET/CT. Progression-free survival (PFS) and overall survival (OS) were analyzed and compared using Kaplan-Meier survival curves.

RESULTS

Among the 40 newly diagnosed MM patients [median age: 56.5 years (IQR 45.25 to 63.75); 24 men], 68 Ga-Pentixafor PET/CT was positive in a greater proportion of patients than 18 F-FDG PET/CT [90% (36/40) vs. 67.5% (27/40); P =0.02] thus, adequately evaluated response in additional 27.5% (11/40) of cases. Using the proposed criteria for 68 Ga-Pentixafor PET/CT, significant differences in PFS were observed across response categories [complete response (CR)-not reached, partial response (PR)-26.2 mo, progressive disease (PD)-15.3 mo; P =0.001]. Among patients achieving ≥very good partial response (VGPR) as per IMWG, those with positive 68 Ga-Pentixafor PET/CT had shorter PFS compared with those with negative findings (median PFS: 34.2 mo vs. not reached; P =0.056), whereas no significant difference was noted with 18 F-FDG PET/CT ( P =0.68). In addition, on follow-up of patients with negative 18 F-FDG at the response, those with discordant 68 Ga-Pentixafor findings had significantly shorter PFS (17.73 mo vs. not reached; P =0.010) compared with those with concordant negative findings.

CONCLUSIONS

68 Ga-Pentixafor PET/CT offers a more accurate assessment of treatment response and prognosis in MM patients, adding valuable information beyond the IMWG and 18 F-FDG PET/CT-based criteria.

Whole-body MRI Versus [18F]FDG PET/CT in Diagnosing and Monitoring Plasmacytomas: A Comparative Study

BACKGROUND/OBJECTIVES

Current guidelines recommend [18F]FDG PET/CT as the preferred imaging modality for suspected extramedullary bone plasmacytomas, while whole-body magnetic resonance imaging (WB-MRI) is indicated for solitary bone plasmacytomas. Despite these recommendations, the available evidence comparing the diagnostic efficacy of both techniques remains limited. The aim of this study was to compare the diagnostic efficacy of WB-MRI and [18F]FDG PET/CT in the initial evaluation of plasmacytomas.

METHODS

We performed a multicenter, observational, and retrospective analysis of patients diagnosed with plasmacytoma who underwent WB-MRI and/or [18F]FDG PET/CT as part of their diagnostic workup. Lesions identified were categorized by anatomic location, and concordance between WB-MRI and [18F]FDG PET/CT findings was assessed. The McNemar test and Pearson χ2 test were used to compare detection rates between WB-MRI and [18F]FDG PET/CT.

RESULTS

The study included 73 patients (33 men) recruited between 2012 and 2023, age range 30-94 years (mean 63.4 ± 12.2 y). Of these, 56 patients underwent both diagnostic tests. Diagnoses revealed solitary plasmacytoma in 16 patients, concurrent multiple myeloma (MM) and plasmacytoma in 18 patients, and plasmacytoma in 22 patients with a prior MM history. Out of the 56 plasmacytomas, 40 were osseous and 16 were extramedullary. WB-MRI detected 98.2% of plasmacytomas compared with 83.9% for [18F]FDG PET/CT, with a statistically significant difference of OR 9 (95% CI: 1.2-394.5), P=0.021. Concordance was very high for osseous plasmacytomas but moderate for extramedullary plasmacytomas.

CONCLUSIONS

These findings suggest WB-MRI is an alternative to [18F]FDG PET/CT for detecting plasmacytomas. A comprehensive clinical and radiologic assessment is essential for the optimal evaluation of patients with plasmacytoma.

Prognostic value of [18F]fluorodeoxyglucose-PET/MRI(CT) novel interpretation criteria (IMPeTUs) in multiple myeloma

PURPOSE

[18F]fluorodeoxyglucose (FDG)-PET is a powerful tool to evaluate prognosis in multiple myeloma (MM). The development of systematic and reproducible standard interpretation criteria is crucial for the effective application of FDG-PET in MM. A new set of criteria-Italian Myeloma criteria for PET Use (IMPeTUs)-has standardized PET evaluation in MM. However, the prognostic value of IMPeTUs score remains unknown.

METHODS

A total of 58 patients with newly diagnosed multiple myeloma (NDMM) who underwent both [18F]FDG-PET/MRI and PET/CT examinations at diagnosis were enrolled (ChiCTR1900022597). All patients completed a 42-month follow-up. The prognostic value of the PET/MRI (or PET/CT) IMPeTUs score in predicting progression-free (PFS) and overall (OS) survival was compared with that of individual laboratory parameters and the maximum standardized uptake value (SUVmax). Kaplan-Meier method was used for survival analysis. Univariate and multivariate analyses of prognostic factors were conducted using Cox regression.

RESULTS

ROC curves demonstrated that the area under the curve for the PET/MRI IMPeTUs score was 0.760, exceeding that of the PET/CT IMPeTUs score (0.711), PET/CT BM SUVmax (0.649), PET/MRI BM SUVmax (0.575), bone marrow plasma cells (0.500), and β2-microglobulin (0.501). Univariate analysis and Kaplan-Meier analysis showed that a PET/MRI IMPeTUs score ≥ 13 and PET/CT IMPeTUs score ≥ 10 were significantly associated with worse PFS. Cox multivariate analysis showed that a PET/MRI IMPeTUs score ≥ 13 was an independent risk factor for PFS.

CONCLUSION

IMPeTUs standardized [18F]FDG-PET/MRI and PET/CT readings in MM. The IMPeTUs score is crucial for predicting MM prognosis, performing better than SUVmax and clinical indicators.

CLINICAL TRIAL REGISTRATION

ChiCTR1900022597, Registered on 18 April 2019.

Diagnostic Innovations: Advances in imaging techniques for diagnosis and follow-up of multiple myeloma

Introduction

The International Myeloma Working Group (IMWG) defines myeloma related bone disease (MBD) as a diagnostic criterion for symptomatic multiple myeloma (MM) as the presence of osteolytic lesions ≥ 5 mm or more than one focal lesion (FL) ≥ 5 mm by magnetic resonance imaging (MRI). Whole-body low-dose CT (WBLDCT) is recommended as the first-choice imaging technique for the diagnosis of MBD with 18F-fluorodeoxyglucose-positron emission tomography/CT (18F-FDG-PET/CT) being considered a possible alternative at staging, whereas use of MRI studies is recommended in cases without myeloma-defining events (MDEs) in order to exclude the presence of FLs. Furthermore, use of 18F-FDG-PET/CT is recommended in response assessment, to be integrated with hematologic response and bone marrow minimal residual disease (MRD).

Areas covered

In this paper, we review novel functional imaging techniques in MM, particularly focusing on their advantages, limits, applications and comparisons with 18F-FDG-PET/CT or other standardized imaging techniques.

Conclusions

Combining both morphological and functional imaging, 18F-FDG-PET/CT is currently considered a standard imaging technique in MM for staging (despite false positive or negative results) and response assessment. The introduction of novel functional imaging techniques, as whole-body diffusion-weighted magnetic resonance imaging (WB-DWI-MRI), or novel PET tracers might be useful in overcoming these limits. Future studies will give more information on the complementarity of these imaging techniques or whether one of them might become a new gold standard in MM.

Serum Albumin Alters [ 18 F]FDG Activity in the Liver and Blood Pool

Objective  This study aims to investigate the correlation between the 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG) activity of the liver and blood pool, and the serum albumin. Methods  A retrospective analysis was conducted on adult patients who underwent [ 18 F]FDG positron emission tomography/computed tomography at the Nuclear Medicine Unit of a hospital in Hong Kong between January 1, 2023, and March 31, 2023. The mean standardized uptake value normalized to lean body mass (SULmean) was measured in the liver and blood pool. Pearson's correlation analyses between the SULmean of reference regions and serum albumin were performed. Multiple linear regression was used to analyze the effects of serum albumin and other parameters as the independent predictors on SULmean of the reference regions. Results  A total of 146 patients were included, with their SULmean of the liver and blood pool showing significantly positive correlations with serum albumin ( r  = 0.393, p  < 0.001 and r  = 0.207, p  = 0.012, respectively). Multiple linear regression analyses confirmed serum albumin as an independent variable on SULmean of the liver and blood pool ( p  < 0.001 and p  = 0.014, respectively). Conclusion  Serum albumin alters [ 18 F]FDG biodistribution in the liver and blood pool. The decrease in liver background activity in patients with low serum albumin may produce a higher false-positive rate of lesion detection, particularly when there is a drop of serum albumin in serial scans. Nuclear medicine physicians should be cautious of image interpretation.

Clinical impact of [18F]FDG-PET/CT in ARI0002h treatment, a CAR-T against BCMA for relapsed/refractory multiple myeloma

ABSTRACT

Multiple myeloma (MM) remains incurable, with poor outcomes in heavily pretreated patients. Chimeric antigen receptor (CAR) T-cell therapy has emerged as a promising treatment; however, outcomes after such therapy in patients with soft-tissue plasmacytomas and other bone lesions remain poorly understood. This study included 63 patients with relapsed/refractory MM treated either in the CARTBCMA-HCB-01 clinical trial (ARI0002h; academic B-cell maturation antigen [BCMA]-targeted CAR T-cell therapy) or in compassionate use. The aim was to evaluate the impact of soft-tissue involvement (extramedullary [EMD] and paraskeletal [PS] plasmacytomas) in response, survival and safety. Baseline [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) from 5 participating centers were reviewed centrally. Of 63 patients, 52.4% presented plasmacytomas at the time of inclusion (21 PS, exclusively; and 12 EMD). Per responses, there were no significant differences between patients with and without plasmacytomas. A correlation was present between International Myeloma Working Group responses and those obtained by [18F]FDG-PET/CT at day 100 (Bologna criteria). No differences were observed in progression-free survival (PFS) or overall survival (OS) between patients with or without plasmacytomas. However, both PFS and OS were significantly shorter in patients with EMD. Interestingly, [18F]FDG-PET/CT response assessed on day 100, in accordance with the Bologna criteria, was predictive of survival outcomes. A metabolic tumor volume of ≥25 cm3 at baseline [18F]FDG-PET/CT was associated with earlier disease progression and shorter OS. These results highlight the importance of EMD evaluation by [18F]FDG-PET/CT before and after CAR T-cell infusion. This trial was registered at www.ClinicalTrials.gov as #NCT04309981; and EudraCT, 2019-001472-11.

Real-World Evidence on Prognostic Value of MRD in Multiple Myeloma Using Flow Cytometry

Minimal residual disease (MRD) is one of the most important prognostic factors in multiple myeloma (MM) and a valid surrogate for progression-free survival (PFS) and overall survival (OS). Recently, MRD negativity was approved as an early clinical endpoint for accelerated drug approval in MM. Nevertheless, there is limited evidence of MRD utility in real-world setting. In this retrospective multicenter study, we report outcomes of 331 newly diagnosed MM patients with MRD evaluation at Day+100 after autologous stem cell transplantation using flow cytometry with a median limit of detection of 0.001%. MRD negativity was reached in 47% of patients and was associated with significantly prolonged median PFS (49.2 months vs. 18.4 months; hazard ratios (HR) = 0.37; p < 0.001) and OS (not reached vs. 74.9 months; HR = 0.50; p = 0.007). Achieving MRD negativity was associated with PFS improvements regardless of age, International Staging System (ISS) stage, lactate dedydrogenase (LDH) level, or cytogenetic risk. Importantly, MRD positive patients benefited from lenalidomide maintenance versus no maintenance (18-months PFS: 81% vs. 46%; HR = 0.24; p = 0.002) while in MRD negative patients such benefit was not observed (p = 0.747). The outcomes of our real-world study recapitulate results from clinical trials including meta-analyses and support the idea that MRD positive patients profit more from lenalidomide maintenance than MRD negative ones.

EANM guidelines on the use of [18F]FDG PET/CT in diagnosis, staging, prognostication, therapy assessment, and restaging of plasma cell disorders

We provide updated guidance and standards for the indication, acquisition, and interpretation of [18F]FDG PET/CT for plasma cell disorders. Procedures and characteristics are reported and different scenarios for the clinical use of [18F]FDG PET/CT are discussed. This document provides clinicians and technicians with the best available evidence to support the implementation of [18F]FDG PET/CT imaging in routine practice and future research.

IMPeTUs parameters correlate with clinical features in newly diagnosed multiple myeloma

Objectives

To investigate the correlations between IMPeTUs-based 18 F-FDG PET/CT parameters and clinical features in patients with newly diagnosed multiple myeloma (MM).

Materials and methods

PET/CT were analysed according to the IMPeTUs criteria. We correlated these PET/CT parameters with known clinically relevant features, bone marrow plasma cell (BMPC) infiltration rate and the presence of cytogenetic abnormalities.

Results

A total of 149 patients (86 males, 63 females; mean age, 59.9 ± 9.7 years) were included. Bone marrow metabolic state correlated with the most clinical features including hemoglobin (rho=-0.23, p=0.004), FLC ratio (rho=0.24, p=0.005), β2 M (rho=0.28, p=0.001), CRP (rho=0.25, p=0.003), serum calcium (rho=0.22, p=0.02), serum creatinine (rho=0.24, p=0.004) and BMPC (rho=0.21, p=0.003). Besides, the level of hemoglobin was significant lower (0.043), and the levels of FLC ratio (0.037), β2 M (p=0.024), CRP (p=0.05), and BMPC (p=0.043) were significant higher in patients having hypermetabolism in limbs and ribs. Hottest bone lesion Deauville criteria had a moderate correlation with CRP (rho=0.27, p=0.001) and serum calcium (rho=0.25, p=0.01).

Conclusion

Several IMPeTUs-based PET/CT parameters showed significant correlations with clinical features reflecting disease burden and biology, suggesting that these new criteria can be used in the risk stratification in MM patients.

Symptomatic Myeloma: PET, Whole-Body MR Imaging with Diffusion-Weighted Imaging or Both

According to international guidelines, patients with suspected myeloma should primarily undergo low-dose whole-body computed tomography (CT) for diagnostic purposes. To optimize sensitivity and specificity and enable treatment response assessment, whole-body MR (WB-MR) imaging should include diffusion-weighted imaging with apparent diffusion coefficient maps and T1-weighted Dixon sequences with bone marrow Fat Fraction Quantification. At baseline WB-MR imaging shows greater sensitivity for the detecting focal lesions and diffuse bone marrow infiltration pattern than 18F-fluorodeoxyglucose PET-CT, which is considered of choice for evaluating response to treatment and minimal residual disease and imaging of extramedullary disease.

Advanced imaging for earlier diagnosis and morbidity prevention in multiple myeloma: A British Society of Haematology and UK Myeloma Society Good Practice Paper

This Good Practice Paper provides recommendations for the use of advanced imaging for earlier diagnosis and morbidity prevention in multiple myeloma. It describes how advanced imaging contributes to optimal healthcare resource utilisation by in newly diagnosed and relapsed myeloma, and provides a perspective on future directions of myeloma imaging, including machine learning assisted reporting.

Development of 18F-Fluoromisonidazole Hypoxia PET/CT Diagnostic Interpretation Criteria and Validation of Interreader Reliability, Reproducibility, and Performance

Tumor hypoxia, an integral biomarker to guide radiotherapy, can be imaged with 18F-fluoromisonidazole (18F-FMISO) hypoxia PET. One major obstacle to its broader application is the lack of standardized interpretation criteria. We sought to develop and validate practical interpretation criteria and a dedicated training protocol for nuclear medicine physicians to interpret 18F-FMISO hypoxia PET. Methods: We randomly selected 123 patients with human papillomavirus-positive oropharyngeal cancer enrolled in a phase II trial who underwent 123 18F-FDG PET/CT and 134 18F-FMISO PET/CT scans. Four independent nuclear medicine physicians with no 18F-FMISO experience read the scans. Interpretation by a fifth nuclear medicine physician with over 2 decades of 18F-FMISO experience was the reference standard. Performance was evaluated after initial instruction and subsequent dedicated training. Scans were considered positive for hypoxia by visual assessment if 18F-FMISO uptake was greater than floor-of-mouth uptake. Additionally, SUVmax was determined to evaluate whether quantitative assessment using tumor-to-background ratios could be helpful to define hypoxia positivity. Results: Visual assessment produced a mean sensitivity and specificity of 77.3% and 80.9%, with fair interreader agreement (κ = 0.34), after initial instruction. After dedicated training, mean sensitivity and specificity improved to 97.6% and 86.9%, with almost perfect agreement (κ = 0.86). Quantitative assessment with an estimated best SUVmax ratio threshold of more than 1.2 to define hypoxia positivity produced a mean sensitivity and specificity of 56.8% and 95.9%, respectively, with substantial interreader agreement (κ = 0.66), after initial instruction. After dedicated training, mean sensitivity improved to 89.6% whereas mean specificity remained high at 95.3%, with near-perfect interreader agreement (κ = 0.86). Conclusion: Nuclear medicine physicians without 18F-FMISO hypoxia PET reading experience demonstrate much improved interreader agreement with dedicated training using specific interpretation criteria.

Artificial intelligence-based, volumetric assessment of the bone marrow metabolic activity in [18F]FDG PET/CT predicts survival in multiple myeloma

PURPOSE

Multiple myeloma (MM) is a highly heterogeneous disease with wide variations in patient outcome. [18F]FDG PET/CT can provide prognostic information in MM, but it is hampered by issues regarding standardization of scan interpretation. Our group has recently demonstrated the feasibility of automated, volumetric assessment of bone marrow (BM) metabolic activity on PET/CT using a novel artificial intelligence (AI)-based tool. Accordingly, the aim of the current study is to investigate the prognostic role of whole-body calculations of BM metabolism in patients with newly diagnosed MM using this AI tool.

MATERIALS AND METHODS

Forty-four, previously untreated MM patients underwent whole-body [18F]FDG PET/CT. Automated PET/CT image segmentation and volumetric quantification of BM metabolism were based on an initial CT-based segmentation of the skeleton, its transfer to the standardized uptake value (SUV) PET images, subsequent application of different SUV thresholds, and refinement of the resulting regions using postprocessing. In the present analysis, ten different uptake thresholds (AI approaches), based on reference organs or absolute SUV values, were applied for definition of pathological tracer uptake and subsequent calculation of the whole-body metabolic tumor volume (MTV) and total lesion glycolysis (TLG). Correlation analysis was performed between the automated PET values and histopathological results of the BM as well as patients' progression-free survival (PFS) and overall survival (OS). Receiver operating characteristic (ROC) curve analysis was used to investigate the discrimination performance of MTV and TLG for prediction of 2-year PFS. The prognostic performance of the new Italian Myeloma criteria for PET Use (IMPeTUs) was also investigated.

RESULTS

Median follow-up [95% CI] of the patient cohort was 110 months [105-123 months]. AI-based BM segmentation and calculation of MTV and TLG were feasible in all patients. A significant, positive, moderate correlation was observed between the automated quantitative whole-body PET/CT parameters, MTV and TLG, and BM plasma cell infiltration for all ten [18F]FDG uptake thresholds. With regard to PFS, univariable analysis for both MTV and TLG predicted patient outcome reasonably well for all AI approaches. Adjusting for cytogenetic abnormalities and BM plasma cell infiltration rate, multivariable analysis also showed prognostic significance for high MTV, which defined pathological [18F]FDG uptake in the BM via the liver. In terms of OS, univariable and multivariable analysis showed that whole-body MTV, again mainly using liver uptake as reference, was significantly associated with shorter survival. In line with these findings, ROC curve analysis showed that MTV and TLG, assessed using liver-based cut-offs, could predict 2-year PFS rates. The application of IMPeTUs showed that the number of focal hypermetabolic BM lesions and extramedullary disease had an adverse effect on PFS.

CONCLUSIONS

The AI-based, whole-body calculations of BM metabolism via the parameters MTV and TLG not only correlate with the degree of BM plasma cell infiltration, but also predict patient survival in MM. In particular, the parameter MTV, using the liver uptake as reference for BM segmentation, provides solid prognostic information for disease progression. In addition to highlighting the prognostic significance of automated, global volumetric estimation of metabolic tumor burden, these data open up new perspectives towards solving the complex problem of interpreting PET scans in MM with a simple, fast, and robust method that is not affected by operator-dependent interventions.

Impact of extramedullary multiple myeloma on outcomes with idecabtagene vicleucel

Idecabtagene vicleucel (Ide-cel) has demonstrated excellent efficacy and durable responses in patients with relapsed/refractory multiple myeloma (RRMM). However, the outcomes with ide-cel in patients with extramedullary disease (EMD) remain incompletely characterized. We included patients with RRMM treated with ide-cel between May 2021 and April 2023 across 11 US academic institutions. Visceral or soft tissue lesions non-contiguous from bone was classified as EMD. Time-to-event analyses were performed from date of ide-cel infusion. Among 351 patients, 84 (24%) had EMD prior to infusion. The median follow-up from ide-cel infusion was 18.2 months (95% CI: 17-19.3). The day 90 overall response rates (ORR) were 52% vs. 82% for the EMD and non-EMD cohorts, respectively (p < 0.001). The median progression-free survival (PFS) was 5.3 months (95% CI: 4.1-6.9) for the EMD cohort vs. 11.1 months (95% CI: 9.2-12.6; p < 0.0001) for the non-EMD cohort. In a multivariable analysis, EMD was an independent predictor of inferior PFS [hazard ratio 1.5 (1.1-2.2), p = 0.02]. The median overall survival was 14.8 months [95% CI: 9-Not reached (NR)] vs. 26.9 months (26.3 vs. NR, p = 0.006) for the EMD and non-EMD cohorts, respectively. Extramedullary disease represents an independent predictor of inferior day 90 ORR and PFS among patients treated with ide-cel.

Prognostic value of visual IMPeTUs criteria and metabolic tumor burden at baseline [18F]FDG PET/CT in patients with newly diagnosed multiple myeloma

BACKGROUND

2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) positron emission tomography combined with low-dose computed tomography (PET/CT) can be used at diagnosis to identify myeloma-defining events and also provides prognostic factors. The aim of this study was to assess the prognostic significance of baseline [18F]FDG PET/CT visual IMPeTUs (Italian myeloma criteria for PET Use)-based parameters and/or total metabolic tumor volume (TMTV) in a single-center population of patients with newly diagnosed multiple myeloma (NDMM) eligible for transplantation.

METHODS

Patients with MM who underwent a baseline [18F]FDG PET/CT were retrospectively selected from a large internal database of the University Hospital of Liege (Liege, Belgium). Initially, all PET/CT images were visually analyzed using IMPeTUs criteria, followed by delineation of TMTV using a semi-automatic lesion delineation workflow, including [18F]FDG-positive MM focal lesions (FL) with an absolute SUV threshold set at 4.0. In a first step, to ensure PET/CT scans accurate reporting, the agreement between two nuclear medicine physicians with distinct experience was assessed. In the second step, univariable and multivariable analyses were conducted to determine the prognostic significance of [18F]FDG PET/CT parameters on progression free survival (PFS) and overall survival (OS), respectively.

RESULTS

A total of 40 patients with NDMM were included in the study. The observers agreement in the analysis [18F]FDG PET/CT images was substantial for the presence of spine FL, extra spine FL, at least one fracture and paramedullary disease (Cohen's kappa 0.79, 0.87, 0.75 and 0.64, respectively). For the presence of skull FL and extramedullary disease the agreement was moderate (Cohen's kappa 0.56 and 0.53, respectively). Among [18F]FDG PET/CT parameters, a high number of delineated volumes of interest (VOI) using the SUV4.0 threshold was the only independent prognostic factor associated with PFS [HR (95% CI): 1.03 (1.004-1.05), P = 0.019] while a high number of FL (n > 10; F group 4) was the only independent prognostic factor associated with OS [HR (95% CI): 19.10 (1.90-191.95), P = 0.01].

CONCLUSION

Our work confirms the reproducibility IMPeTUs criteria. Furthermore, it demonstrates that a high number of FL (n > 10; IMPeTUs F group 4), reflecting a high [18F]FDG-avid tumor burden, is an independent prognostic factor for OS. The prognostic value of the TMTV delineated using a SUV4.0 threshold was not significant. Nevertheless, the count of delineated [18F]FDG-avid lesions VOI using a SUV4.0 threshold was an independent prognostic factor for PFS.

Analysis of baseline circulating tumor cells integrated with PET/CT findings in transplant-ineligible multiple myeloma

ABSTRACT

We aimed to improve prognostic predictors in patients with transplant-ineligible multiple myeloma (TIE-MM) by combining baseline circulating clonal tumor cells (CTCs) and positron emission tomography/computed tomography (PET/CT) findings. The factors associated with prognosis were retrospectively investigated in 126 patients with TIE-MM who underwent CTC quantification by multiparameter flow cytometry and PET/CT at the initial presentation. The total lesion glycolysis (TLG) level was calculated using the Metavol software. The median percentage of CTC was 0.06% (range, 0%-4.82%), and 54 patients (42.9%) demonstrated high CTC levels. High CTC levels were associated with significantly poorer progression-free survival (PFS, 2-year 43.4% vs 68.1%; P < .001) and overall survival (OS, 5-year 39.0% vs 68.3%; P < .001). Similarly, high TLG levels significantly worsened the PFS (2-year, 41.2% vs 67.6%; P = .038) and OS (5-year, 37.7% vs 63.1%; P = .019). The multivariate analyses showed that Revised International Staging System (R-ISS) III, high CTC and TLG levels, and complete response were significant prognostic factors for PFS and OS. A novel predictive model was constructed using CTCs, TLG, and R-ISS III. The patients were stratified into 3 groups according to the number of risk factors, revealing an extremely high-risk group with a 2-year PFS of 0% and a 5-year OS of 20%. Patients without any high-risk features had better prognosis, with a 2-year PFS of 78.6% and a 5-year OS of 79.5%. The combination of CTCs and volumetric assessment of PET/CT at diagnosis augments the existing stratification systems and may pave the way for a risk-adapted treatment approach.

Imaging of Multiple Myeloma: Present and Future

Multiple myeloma (MM) is the second most common adult hematologic malignancy, and early intervention increases survival in asymptomatic high-risk patients. Imaging is crucial for the diagnosis and follow-up of MM, as the detection of bone and bone marrow lesions often dictates the decision to start treatment. Low-dose whole-body computed tomography (CT) is the modality of choice for the initial assessment, and dual-energy CT is a developing technique with the potential for detecting non-lytic marrow infiltration and evaluating the response to treatment. Magnetic resonance imaging (MRI) is more sensitive and specific than 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for the detection of small focal lesions and diffuse marrow infiltration. However, FDG-PET/CT is recommended as the modality of choice for follow-up. Recently, diffusion-weighted MRI has become a new technique for the quantitative assessment of disease burden and therapy response. Although not widespread, we address current proposals for structured reporting to promote standardization and diminish variations. This review provides an up-to-date overview of MM imaging, indications, advantages, limitations, and recommended reporting of each technique. We also cover the main differential diagnosis and pitfalls and discuss the ongoing controversies and future directions, such as PET-MRI and artificial intelligence.

Clinical factors associated with autologous stem cell transplantation outcomes in multiple myeloma: upfront transplant with MEL200 remains the standard of care

Autologous stem cell transplantation (ASCT) remains the mainstay of the treatment in newly diagnosed transplant-eligible multiple myeloma (MM) patients. This retrospective study was performed to investigate the potential prognostic markers which may modify transplant course in a total of 256 ASCT recipients [median age: 58 (30-74) years; male/female: 138/118], including pretransplant (PET0) and day + 60 (PET2) PET/CT assessments and comparative analysis of melphalan (Mel) dose. Better responses with significantly higher complete response/very good partial response rates were achieved in patients who proceeded to transplant within 301 days from diagnosis (p < 0.001). Patients who had received < 1.5 lines of treatment prior to transplant had significantly higher probability of overall survival (OS) (p = 0.004) and progression-free survival (PFS) (p < 0.001). The probability of OS was significantly higher in patients with low Eastern Cooperative Oncology Group (ECOG) performance score (PS = 0-1) (p = 0.003) and HCT-Comorbidity Index (HCT-CI = 0) (p = 0.011). The number of involved areas (p = 0.028) and maximum standardized uptake value (SUVmax) (p = 0.021) in PET0 represented significant impact on OS. The probabilities of OS (p < 0.001) and PFS (p = 0.01) were significantly better with Mel200 mg/m2 conditioning compared to Mel140 mg/m2. Conditioning with Mel200 mg/m2, early and upfront ASCT and low pretransplant treatment burden were found to be significantly associated with ASCT outcome in MM patients. Despite its predictor impact on survival and prognosis, further studies are warranted to standardize PET/CT-based response assessments before being used as a guide for treatment decisions in clinical practice.

Evaluation of a semi-automated approach for FDG PET image analysis for routine clinical application in patients with multiple myeloma

BACKGROUND

FDG PET/CT is a tool for assessing response to therapy in various cancers, and may provide an earlier biomarker of clinical response. We developed a novel semi-automated approach for analyzing FDG PET/CT images in patients with multiple myeloma (MM) to standardize FDG PET application.

METHODS

Patients (n = 8) with relapsed/refractory MM from the Phase 2 study (NCT02899052) of venetoclax plus carfilzomib and dexamethasone underwent FDG PET/CT at baseline and up to two timepoints during treatment. Images were processed using an established automated segmentation algorithm, with the modification that a red marrow region in an unaffected lumbar vertebra was used to define background standardized uptake value normalized to lean body mass (SUL) threshold above which uptake was considered disease-specific uptake. This approach was compared to lesion segmentation, and to International Myeloma Working Group (IMWG) response criteria, including minimal residual disease (MRD).

RESULTS

The two FDG PET analysis techniques agreed on evaluation of patient-level SULpeak for 67% of scans. In the metabolic response assessment per PET Response Criteria in Solid Tumors (PERCIST), the two techniques agreed in 75% of patients. Differences between techniques occurred in low-uptake lesions due to greater reader sensitivity to lesions with uptake marginally above background. PERCIST outcomes were generally in agreement with IMWC and MRD.

CONCLUSIONS

This semi-automated analysis was in high agreement with standard approaches for detecting response to MM therapy. This proof-of-concept study suggests that larger studies should be conducted to confirm how FDG PET analysis may aid early response detection in MM.

How do we image patients with multiple myeloma and precursor states?

Advances in morphological and functional imaging have led to superior detection of early bone disease, bone marrow infiltration, paramedullary and extramedullary involvement in multiple myeloma. The two functional imaging modalities that are most widely used and standardized are 18F-fluorodeoxyglucose-Positron emission tomography/computed tomography (FDG PET/CT) and whole-body magnetic resonance imaging with diffusion-weighted imaging (WB DW-MRI). Both prospective and retrospective studies have demonstrated that WB DW-MRI is more sensitive than PET/CT in the detection of baseline tumour burden and to assess response after therapy. In patients with smouldering multiple myeloma, WB DW-MRI is now the preferred imaging modality to rule out two or more unequivocal lesions which would be considered a myeloma-defining event by the updated international myeloma working group (IMWG) criteria. In addition to sensitive detection of baseline tumour burden, both PET/CT and WB DW-MRI have been successfully used for monitoring response to therapy and provide information that is complementary to IMWG response assessment and bone marrow minimal residual disease. In this article, we present 3 vignettes illustrating how we approach the use of modern imaging in the management of patients with multiple myeloma and precursor states, with a specific focus on recent data that have emerged since the publication of the IMWG consensus guideline on imaging. We have utilized data from prospective and retrospective studies to provide a rationale for our approach to imaging in these clinical scenarios and highlighted knowledge gaps requiring future investigation.

Intensifying treatment in PET-positive multiple myeloma patients after upfront autologous stem cell transplantation

18F-Fluorodeoxyglucose positron emission tomography/computed tomography (PET) positivity after first-line treatment with autologous stem cell transplantation (ASCT) in multiple myeloma is strongly correlated with reduced progression-free and overall survival. However, PET-positive patients who achieve PET negativity after treatment seem to have comparable outcomes to patients who were PET negative at diagnosis. Hence, giving PET-positive patients additional treatment may improve their outcome. In this phase II study, we screened first-line patients with very good partial response (VGPR) or better after ASCT with PET. PET-positive patients received four 28-day cycles of carfilzomib-lenalidomide-dexamethasone (KRd). Flow cytometry-based minimal residual disease (MRD) analysis was performed before and after treatment for correlation with PET. Overall, 159 patients were screened with PET. A total of 53 patients (33%) were PET positive and 57% of PET-positive patients were MRD negative, demonstrating that these response assessments are complementary. KRd consolidation converted 33% of PET-positive patients into PET negativity. MRD-negative patients were more likely to convert than MRD-positive patients. In summary, PET after ASCT detected residual disease in a substantial proportion of patients in VGPR or better, even in patients who were MRD negative, and KRd consolidation treatment changed PET status in 33% of patients.

New Developments in Myeloma Treatment and Response Assessment

Recent innovative strategies have dramatically redefined the therapeutic landscape for treating multiple myeloma patients. In particular, the development and application of immunotherapy and high-dose therapy have demonstrated high response rates and have prolonged remission duration. Over the past decade, new morphologic or hybrid imaging techniques have gradually replaced conventional skeletal surveys. PET/CT using 18F-FDG is a powerful imaging tool for the workup at diagnosis and for therapeutic evaluation allowing medullary and extramedullary assessment. The independent negative prognostic value for progression-free and overall survival derived from baseline PET-derived parameters such as the presence of extramedullary disease or paramedullary disease, as well as the number of focal bone lesions and SUVmax, has been reported in several large prospective studies. During therapeutic evaluation, 18F-FDG PET/CT is considered the reference imaging technique because it can be performed much earlier than MRI, which lacks specificity. Persistence of significant abnormal 18F-FDG uptake after therapy is an independent negative prognostic factor, and 18F-FDG PET/CT and medullary flow cytometry are complementary tools for detecting minimal residual disease before maintenance therapy. The definition of a PET metabolic complete response has recently been standardized and the interpretation criteria harmonized. The development of advanced PET analysis and radiomics using machine learning, as well as hybrid imaging with PET/MRI, offers new perspectives for multiple myeloma imaging. Most recently, innovative radiopharmaceuticals such as C-X-C chemokine receptor type 4-targeted small molecules and anti-CD38 radiolabeled antibodies have shown promising results for tumor phenotype imaging and as potential theranostics.

Minimal Residual Disease in Multiple Myeloma: Past, Present, and Future

Responses to treatment have improved over the last decades for patients with multiple myeloma. This is a consequence of the introduction of new drugs that have been successfully combined in different clinical contexts: newly diagnosed, transplant-eligible or ineligible patients, as well as in the relapsed/refractory setting. However, a great proportion of patients continue to relapse, even those achieving complete response, which underlines the need for updated response criteria. In 2014, the international myeloma working group established new levels of response, prompting the evaluation of minimal residual disease (MRD) for those patients already in complete or stringent complete response as defined by conventional serological assessments: the absence of tumor plasma cells in 100,000 total cells or more define molecular and immunophenotypic responses by next-generation sequencing and flow cytometry, respectively. In this review, we describe all the potential methods that may be used for MRD detection based on the evidence found in the literature, paying special attention to their advantages and pitfalls from a critical perspective.

Impact of minimal residual disease standardised assessment by FDG-PET/CT in transplant-eligible patients with newly diagnosed multiple myeloma enrolled in the imaging sub-study of the FORTE trial

Background

18F-FDG-PET/CT is the current standard technique to define minimal residual disease (MRD) outside the bone marrow (BM) in multiple myeloma (MM), recently standardised applying the Deauville scores (DS) to focal lesions (FS) and bone marrow uptake (BMS) and defining the complete metabolic response (CMR) as uptake below the liver background (DS <4).

Methods

In this analysis, we aimed at confirming the role of CMR, and complementarity with BM multiparameter flow cytometry (MFC) at 10^-5, in an independent cohort of newly diagnosed transplant-eligible MM patients previously enrolled in the phase II randomised FORTE trial. 109 of the 474 global patients enrolled in the trial between February 23, 2015, and April 5, 2017, who had paired PET/CT (performed at baseline [B] and preceding maintenance therapy [PM]) and MFC evaluation, were included in this analysis.

Findings

At B, 93% of patients had focal lesions within the bones (FS ≥4 in 89%) and 99% increased BM uptake (BMS ≥4 in 61%). At PM, CMR was achieved in 63% of patients, which was a strong predictor for prolonged PFS in univariate analysis at landmark time PM (HR 0.40, P = 0.0065) and in Cox multivariate analysis (HR 0.31, P = 0.0023). Regarding OS, a trend in favour of CMR was present in univariate (HR 0.44, P = 0.094), and Cox multivariate model (HR 0.17, P = 0.0037). Patients achieving both PET/CT CMR and MFC negativity at PM showed significantly extended PFS in univariate (HR 0.45, P = 0.020) and multivariate analysis (HR 0.41, P = 0.015).

Interpretation

We herein confirm the applicability and validity of DS criteria to define CMR and its prognostic relevance and complementarity with MFC at the BM level.

Funding

Amgen, Celgene/Bristol Myers Squibb, Italian Ministry of Health (RC-2022-2773423).

Deep learning PET/CT-based radiomics integrates clinical data: A feasibility study to distinguish between tuberculosis nodules and lung cancer

BACKGROUND

Radiomic diagnosis models generally consider only a single dimension of information, leading to limitations in their diagnostic accuracy and reliability. The integration of multiple dimensions of information into the deep learning model have the potential to improve its diagnostic capabilities. The purpose of study was to evaluate the performance of deep learning model in distinguishing tuberculosis (TB) nodules and lung cancer (LC) based on deep learning features, radiomic features, and clinical information.

METHODS

Positron emission tomography (PET) and computed tomography (CT) image data from 97 patients with LC and 77 patients with TB nodules were collected. One hundred radiomic features were extracted from both PET and CT imaging using the pyradiomics platform, and 2048 deep learning features were obtained through a residual neural network approach. Four models included traditional machine learning model with radiomic features as input (traditional radiomics), a deep learning model with separate input of image features (deep convolutional neural networks [DCNN]), a deep learning model with two inputs of radiomic features and deep learning features (radiomics-DCNN) and a deep learning model with inputs of radiomic features and deep learning features and clinical information (integrated model). The models were evaluated using area under the curve (AUC), sensitivity, accuracy, specificity, and F1-score metrics.

RESULTS

The results of the classification of TB nodules and LC showed that the integrated model achieved an AUC of 0.84 (0.82-0.88), sensitivity of 0.85 (0.80-0.88), and specificity of 0.84 (0.83-0.87), performing better than the other models.

CONCLUSION

The integrated model was found to be the best classification model in the diagnosis of TB nodules and solid LC.

Radiomics analysis of bone marrow biopsy locations in [18F]FDG PET/CT images for measurable residual disease assessment in multiple myeloma

The combination of visual assessment of whole body [¹⁸F]FDG PET images and evaluation of bone marrow samples by Multiparameter Flow Cytometry (MFC) or Next-Generation Sequencing (NGS) is currently the most common clinical practice for the detection of Measurable Residual Disease (MRD) in Multiple Myeloma (MM) patients. In this study, radiomic features extracted from the bone marrow biopsy locations are analyzed and compared to those extracted from the whole bone marrow in order to study the representativeness of these biopsy locations in the image-based MRD assessment. Whole body [¹⁸F]FDG PET of 39 patients with newly diagnosed MM were included in the database, and visually evaluated by experts in nuclear medicine. A methodology for the segmentation of biopsy sites from PET images, including sternum and posterior iliac crest, and their subsequent quantification is proposed. First, starting from the bone marrow segmentation, a segmentation of the biopsy sites is performed. Then, segmentations are quantified extracting SUV metrics and radiomic features from the [¹⁸F]FDG PET images and are evaluated by Mann-Whitney U-tests as valuable features differentiating PET+/PET- and MFC+ /MFC- groups. Moreover, correlation between whole bone marrow and biopsy sites is studied by Spearman ρ rank. Classification performance of the radiomics features is evaluated applying seven machine learning algorithms. Statistical analyses reveal that some images features are significant in PET+/PET- differentiation, such as SUV_max, Gray Level Non-Uniformity or Entropy, especially with a balanced database where 16 of the features show a p value < 0.001. Correlation analyses between whole bone marrow and biopsy sites results in significant and acceptable coefficients, with 11 of the variables reaching a correlation coefficient greater than 0.7, with a maximum of 0.853. Machine learning algorithms demonstrate high performances in PET+/PET- classification reaching a maximum AUC of 0.974, but not for MFC+/MFC- classification. The results demonstrate the representativeness of sample sites as well as the effectiveness of extracted features (SUV metrics and radiomic features) from the [¹⁸F]FDG PET images in MRD assessment in MM patients.

2-[ 18 F]FDG PET/CT Flare-up Phenomena Following T-Cell Engager Bispecific Antibody in Multiple Myeloma

ABSTRACT

T-cell-redirecting bispecific antibodies represent a new standard of care for the treatment of triple-class refractory myeloma patients. Here, 2-[ 18 F]FDG PET/CT imaging was performed on a 61-year-old woman with relapsed myeloma to determine metabolic response to talquetamab, a GPRC5DxCD3-bispecific antibody. At day 28, monoclonal (M) component assessment confirmed very good partial response (97% monoclonal protein reduction), whereas 2-[ 18 F]FDG PET/CT imaging revealed early bone flare-up phenomena. At day 84, bone marrow aspirate, M-component assessment, and 2-[ 18 F]FDG PET/CT demonstrated complete response, confirming the early flare-up hypothesis.

Clinical Value of FDG-PET/CT in Multiple Myeloma: An Update

FDG-PET/CT is a standardized imaging technique that has reached a great importance in the management of patients affected by Multiple Myeloma. It is proved, in fact, that it allows a deep evaluation of therapy efficacy and provides several prognostic indexes both at staging and after therapy. For this reason, it is now recognised as a gold standard for therapy assessment. Beside this, in reacent years FDG-PET/CT contribution to the understanding of Multiple Myeloma has progressively grown. Papers have been published analyzing the prognostic value of active disease volume measurement and standardization issues, the meaning of FDG positive paramedullary and extrameduallary disease, the prognostic impact of FDG positive minimal residual disease, the relation between focal lesions and clonal eterogenity of this disease and the comparison with whole body DWI-MR in terms of detection and therapy assessment. These newer aspects not of clinical impact yet, of FDG-PET/CT in Multiple Myeloma will be presented and discussed in this review.

Treatment Strategy for Ultra-High-Risk Multiple Myelomas with Chromosomal Aberrations Considering Minimal Residual Disease Status and Bone Marrow Microenvironment

Despite the development of anti-myeloma therapeutics, such as proteasome inhibitors, immunomodulatory drugs, anti-CD38 monoclonal antibodies, and autologous stem cell transplantation (ASCT), multiple myeloma remains incurable. A trial treatment combining four drugs-daratumumab, carfilzomib, lenalidomide, and dexamethasone-followed by ASCT frequently results in minimal residual disease (MRD) negativity and prevents progressive disease in patients with standard- and high-risk cytogenetics; however, it is insufficient to overcome the poor outcomes in patients with ultra-high-risk chromosomal aberration (UHRCA). In fact, MRD status in autografts can predict clinical outcomes after ASCT. Therefore, the current treatment strategy might be insufficient to overcome the negative impact of UHRCA in patients with MRD positivity after the four-drug induction therapy. High-risk myeloma cells lead to poor clinical outcomes not only by aggressive myeloma behavior but also via the generation of a poor bone marrow microenvironment. Meanwhile, the immune microenvironment effectively suppresses myeloma cells with a low frequency of high-risk cytogenetic abnormalities in early-stage myeloma compared to late-stage myeloma. Therefore, early intervention might be key to improving clinical outcomes in myeloma patients. The purpose of this review is to improve clinical outcomes in patients with UHRCA by considering MRD assessment results and improvement of the microenvironment.

Imaging glucose metabolism to reveal tumor progression

Purpose: To analyze and review the progress of glucose metabolism-based molecular imaging in detecting tumors to guide clinicians for new management strategies. Summary: When metabolic abnormalities occur, termed the Warburg effect, it simultaneously enables excessive cell proliferation and inhibits cell apoptosis. Molecular imaging technology combines molecular biology and cell probe technology to visualize, characterize, and quantify processes at cellular and subcellular levels in vivo. Modern instruments, including molecular biochemistry, data processing, nanotechnology, and image processing, use molecular probes to perform real-time, non-invasive imaging of molecular and cellular events in living organisms. Conclusion: Molecular imaging is a non-invasive method for live detection, dynamic observation, and quantitative assessment of tumor glucose metabolism. It enables in-depth examination of the connection between the tumor microenvironment and tumor growth, providing a reliable assessment technique for scientific and clinical research. This new technique will facilitate the translation of fundamental research into clinical practice.

Standardized classification schemes in reporting oncologic PET/CT

The imaging report is essential for the communication between physicians in patient care. The information it contains must be clear, concise with evidence-based conclusions and sufficient to support clinical decision-making. In recent years, several classification schemes and/or reporting guidelines for PET have been introduced. In this manuscript, we will review the classifications most frequently used in oncology for interpreting and reporting 18F-FDG PET imaging in lymphoma, multiple myeloma, melanoma and head and neck cancers, PSMA-ligand PET imaging for prostate cancer, and 68Ga-DOTA-peptide PET in neuroendocrine tumors (NET).

Experts' consensus on the definition and management of high risk multiple myeloma

High risk multiple myeloma (HRMM) at diagnosis is currently recognized according to the Revised International Staging System (R-ISS) which was set up in 2015. Since then, new clinical and biological prognostic factors have been developed, which could implement the definition of High Risk (HR) category. We conducted a survey in order to identify which additional parameters, both clinical and biological, are considered more useful for the clinical practice and to evaluate if the management of Multiple Myeloma (MM) should change on the basis of the risk category. A questionnaire, consisting of 8 statements, was submitted to 6 Italian experts, from the European Myeloma Network (EMN) Research Italy, using the Delphi method. The colleagues were asked to answer each question using a scale between 0 and 100. If a statement did not reach at least 75 out of 100 points from all the participants, it was rephrased on the basis of the proposal of the experts and resubmitted in a second or further round, until a consensus was reached among all. From the first round of the survey a strong consensus was reached regarding the opportunity to revise the R-ISS including chromosome 1 abnormality, TP53 mutation or deletion, circulating plasma cells by next generation flow and extramedullary plasmacytomas. No consensus was reached for the definition of "double hit" MM and for the application in clinical practice of treatment strategies based on the risk category. In the second round of the Delphi questionnaire, "double-hit" MM was recognized by the association of at least two high-risk cytogenetic or molecular abnormalities. Moreover, the experts agreed to reserve an intensified treatment only to specific conditions, such as plasma cell leukaemia or patients with multiple extramedullary plasmacytomas, while they admitted that there are not sufficient real word data in order to modify treatment on the basis of MRD assessment in clinical practice. This survey suggests that the definition of HRMM should be implemented by additional clinical and biological risk factors, that will be useful to guide treatment in the future.

A comparison of the International Consensus and 5th World Health Organization classifications of mature B-cell lymphomas

Several editions of the World Health Organization (WHO) classifications of lympho-hemopoietic neoplasms in 2001, 2008 and 2017 served as the international standard for diagnosis. Since the 4th WHO edition, here referred as WHO-HAEM4, significant clinico-pathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining diagnostic criteria of several diseases, to upgrade entities previously defined as provisional and to identify new entities. This process has resulted in two recent classifying proposals of lymphoid neoplasms, the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In this paper, we review and compare the two classifications in terms of diagnostic criteria and entity definition, with focus on mature B-cell neoplasms. The main aim is to provide a tool to facilitate the work of pathologists, hematologists and researchers involved in the diagnosis and treatment of lymphomas.

PET-CT in Clinical Adult Oncology: I. Hematologic Malignancies

PET-CT is an advanced imaging modality with many oncologic applications, including staging, assessment of response to therapy, restaging and evaluation of suspected recurrence. The goal of this 6-part series of review articles is to provide practical information to providers and imaging professionals regarding the best use of PET-CT for the more common adult malignancies. In the first article of this series, hematologic malignancies are addressed. The classification of these malignancies will be outlined, with the disclaimer that the classification of lymphomas is constantly evolving. Critical applications, potential pitfalls, and nuances of PET-CT imaging in hematologic malignancies and imaging features of the major categories of these tumors are addressed. Issues of clinical importance that must be reported by the imaging professionals are outlined. The focus of this article is on [¹⁸F] fluorodeoxyglucose (FDG), rather that research tracers or those requiring a local cyclotron. This information will serve as a resource for the appropriate role and limitations of PET-CT in the clinical management of patients with hematological malignancy for health care professionals caring for adult patients with hematologic malignancies. It also serves as a practical guide for imaging providers, including radiologists, nuclear medicine physicians and their trainees.

Functional Imaging in the Evaluation of Treatment Response in Multiple Myeloma: The Role of PET-CT and MRI

Bone disease is among the defining characteristics of symptomatic Multiple Myeloma (MM). Imaging techniques such as fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET/CT) and magnetic resonance imaging (MRI) can identify plasma cell proliferation and quantify disease activity. This function renders these imaging tools as suitable not only for diagnosis, but also for the assessment of bone disease after treatment of MM patients. The aim of this article is to review FDG PET/CT and MRI and their applications, with a focus on their role in treatment response evaluation. MRI emerges as the technique with the highest sensitivity in lesions' detection and PET/CT as the technique with a major impact on prognosis. Their comparison yields different results concerning the best tool to evaluate treatment response. The inhomogeneity of the data suggests the need to address limitations related to these tools with the employment of new techniques and the potential for a complementary use of both PET/CT and MRI to refine the sensitivity and achieve the standards for minimal residual disease (MRD) evaluation.

Unexpected Heterogeneity of Newly Diagnosed Multiple Myeloma Patients with Plasmacytomas

In multiple myeloma (MM), malignant plasma cells infiltrate the bone marrow. In some cases, plasma cells migrate out of the bone marrow creating either para-skeletal plasmacytomas (PS) or infiltrating soft tissues as extramedullary plasmacytomas (EMD). The aim of this study was to define risk groups in newly diagnosed MM (NDMM) patients with PS and EMD plasmacytomas. In total, 523 NDMM patients with PS plasmacytomas and 196 NDMM patients with EMD plasmacytomas were diagnosed in the Czech Republic between 2004 and 2021 using modern imaging methods. Patients’ data were analyzed from the Registry of Monoclonal Gammopathies of the Czech Myeloma Group. In NDMM patients with PS plasmacytomas, we found a subgroup with <5% of bone-marrow plasma cells to have the best prognosis (mPFS: 58.3 months (95% CI: 33.0−NA); mOS: not reached). The subgroup with >5% of bone-marrow plasma cells and ≥3 plasmacytomas had the worst prognosis (mPFS: 19.3 months (95% CI: 13.4−28.8), p < 0.001; mOS: 27.9 months (95% CI: 19.3−67.8), p < 0.001). Our results show association between tumor burden and prognosis of NDMM patients with plasmacytomas. In the case of PS plasmacytomas, NDMM patients with low BM PC infiltration have an excellent prognosis.

Bone marrow segmentation and radiomics analysis of [18F]FDG PET/CT images for measurable residual disease assessment in multiple myeloma

BACKGROUND AND OBJECTIVES

The last few years have been crucial in defining the most appropriate way to quantitatively assess [¹⁸F]FDG PET images in Multiple Myeloma (MM) patients to detect persistent tumor burden. The visual evaluation of images complements the assessment of Measurable Residual Disease (MRD) in bone marrow samples by multiparameter flow cytometry (MFC) or next-generation sequencing (NGS). The aim of this study was to quantify MRD by analyzing quantitative and texture [¹⁸F]FDG PET features.

METHODS

Whole body [¹⁸F]FDG PET of 39 patients with newly diagnosed MM were included in the database, and visually evaluated by experts in nuclear medicine. A segmentation methodology of the skeleton from CT images and an additional manual segmentation tool were proposed, implemented in a software solution including a graphical user interface. Both the compact bone and the spinal canal were removed from the segmentation to obtain only the bone marrow mask. SUV metrics, GLCM, GLRLM, and NGTDM parameters were extracted from the PET images and evaluated by Mann-Whitney U-tests and Spearman ρ rank correlation as valuable features differentiating PET+/PET- and MFC+/MFC- groups. Seven machine learning algorithms were applied for evaluating the classification performance of the extracted features.

RESULTS

Quantitative analysis for PET+/PET- differentiating demonstrated to be significant for most of the variables assessed with Mann-Whitney U-test such as Variance, Energy, and Entropy (p-value = 0.001). Moreover, the quantitative analysis with a balanced database evaluated by Mann-Whitney U-test revealed in even better results with 19 features with p-values < 0.001. On the other hand, radiomics analysis for MFC+/MFC- differentiating demonstrated the necessity of combining MFC evaluation with [¹⁸F]FDG PET assessment in the MRD diagnosis. Machine learning algorithms using the image features for the PET+/PET- classification demonstrated high performance metrics but decreasing for the MFC+/MFC- classification.

CONCLUSIONS

A proof-of-concept for the extraction and evaluation of bone marrow radiomics features of [¹⁸F]FDG PET images was proposed and implemented. The validation showed the possible use of these features for the image-based assessment of MRD.

Comparison of [18F]fluciclovine and [18F]FDG PET/CT in Newly Diagnosed Multiple Myeloma Patients

PURPOSE

[18F]FDG PET/CT in multiple myeloma (MM) is currently the best technology to demonstrate patchy and extramedullary disease. However, [18F]FDG PET has some limitations, and imaging with alternative tracers should be explored. In this study, we aimed to evaluate the performance of [18F]fluciclovine PET compared to [18F]FDG PET in newly diagnosed MM patients.

PROCEDURES

Thirteen newly diagnosed transplant eligible MM patients were imaged both with [18F]FDG PET/CT and [18F]fluciclovine PET/CT within 1 week in a prospective study. The subjects were visually assessed positive or negative for disease. The number of lesions and the SUVmax of selected lesions were measured for both tracers. Furthermore, tracer uptake ratios were obtained by dividing lesion SUVmax by blood or bone marrow SUVmax. Between-group differences and correlations were assessed with paired t-tests and Pearson tests. Bone marrow SUVs were compared to bone marrow plasma cell percentage in biopsy samples.

RESULTS

Nine subjects were assessed positively by [18F]FDG PET (69%) and 12 positives by [18F]fluciclovine PET (92%). All positive subjects had [18F]fluciclovine scans that were qualitatively scored as easier to interpret visually than the [18F]FDG scans. The number of lesions was also higher; seven of nine subjects with distinct hot spots on [18F]fluciclovine PET had fewer or no visible lesions on [18F]FDG PET. The mean lesion SUVmax values were 8.2 and 3.8 for [18F]fluciclovine and [18F]FDG, respectively. The mean tumour to blood values were 6.4 and 2.0 for [18F]fluciclovine and [18F]FDG, and the mean ratios between tumour and bone marrow were 2.1 and 1.5 for [18F]fluciclovine and [18F]FDG. The lesion SUVmax and ratios were significantly higher for [18F]fluciclovine (all p < 0.01). Local [18F]fluciclovine SUVmax or SUVmean values in os ilium and the percentage of plasma cells in bone marrow biopsies were linearly correlated (p = 0.048). There were no significant correlations between [18F]FDG SUVs and plasma cells (p = 0.82).

CONCLUSIONS

Based on this pilot study, [18F]fluciclovine is a promising tracer for MM. The visual and semi-quantitative evaluations indicate that [18F]fluciclovine PET/CT can out-perform [18F]FDG PET/CT at diagnosis.

Paraskeletal and extramedullary plasmacytomas in multiple myeloma at diagnosis and at first relapse: 50-years of experience from an academic institution

From January 1970 to December 2018, 1304 patients were diagnosed with multiple myeloma (MM) at our institution and 256 (19.6%) had plasmacytomas (Ps) (paraskeletal –PPs- 17.6%, extramedullary –EMPs-1.9%). Patients with Ps had lower serum M-protein and less advanced ISS stage than those without. At first relapse, 192 out of 967 patients (19.8%) developed Ps (PPs 14.6%, EMPs 5.1%). The only factor associated with Ps at relapse was the presence of Ps at diagnosis (46% vs 13%, p < 0.00001) with no impact with exposure to novel drugs or previous autologous stem-cell transplantation (ASCT). The median overall survival (OS) was 45, 44 and 20 months for patients without Ps, PPs and EMPs, respectively (p = 0.013). Patients with PPs who underwent ASCT had similar OS than those without Ps (98 vs. 113 months) and significantly longer than those with EMPs (98 vs 47 months, p = 0.006). In patients non-eligible for ASCT the presence of PPs or EMPs was associated with shorter OS compared with patients without Ps (32 vs. 24 vs. 6 months, p = 0.009). In the relapsed setting, a significant survival benefit was observed beyond the year 2000, but still with significant differences among patients without Ps, PPs and EMPs (37 vs 22 vs 16 months, p = 0.003). Importantly, rescue therapy with combinations of proteasome-inhibitors plus immunomodulatory drugs was associated with prolonged OS from first relapse (over 6 years), even in patients with EMPs.

Steps towards a Multiple Myeloma Cure?

Multiple myeloma survival has increased in last 20 years because of new treatments, better clinical management due to novel diagnostic tools such as imaging, and better understanding of the disease, biologically and genetically. Novel drugs have been introduced that act with different therapeutic mechanisms, but so have novel therapeutic strategies such as consolidation and maintenance after autologous stem cell transplant. Imaging (such as PET-CT and MRI) has been applied at diagnosis and after therapy for minimal residual disease monitoring. Multiparametric flow and molecular NGS may detect, with high-sensitivity, residual monoclonal plasma cells in the bone marrow. With this novel therapeutic and biological approach, a considerable fraction of multiple myeloma patients can achieve durable remission or even MGUS-like regression, which can ultimately lead to disease disappearance. The big dogma, “Myeloma is an incurable disease”, is hopefully fading.

Recent developments on the application of molecular probes in multiple myeloma: Beyond [18F]FDG

Multiple myeloma (MM) is a neoplastic plasma cell proliferative disorder characterized by various osteolytic bone destruction as a radiological morphological marker. Functional imaging, particularly nuclear medicine imaging, is a promising method to visualize disease processes before the appearance of structural changes by targeting specific biomarkers related to metabolism ability, tumor microenvironment as well as neoplastic receptors. In addition, by targeting particular antigens with therapeutic antibodies, immuno-PET imaging can support the development of personalized theranostics. At present, various imaging agents have been prepared and evaluated in MM at preclinical and clinical levels. A summary overview of molecular functional imaging in MM is provided, and commonly used radiotracers are characterized.

Multi-parametric whole-body MRI evaluation discerns vital from non-vital multiple myeloma lesions as validated by 18F-FDG and 11C-methionine PET/CT

PURPOSE

We tested a novel multi-parametric (mp) whole body (WB)-MRI evaluation algorithm for medullary lesions in comparison to positron emission tomography (PET) radiotracers ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ¹¹C-methionine (¹¹C-MET).

METHODS AND MATERIALS

This retrospective single-center study included 44 MM patients, who received both ¹⁸F-FDG-PET and WB-MRI within ten days. MRI classified focal lesions as vital when showing 1) significant diffusion-restriction, 2) a fat fraction (FF) less than 20 % and 3) homogenous hypointensity on T2-weighted images. On a lesion-by-lesion level the findings were compared to ¹⁸F-FDG PET by using a 5-point scoring system (analogous to the Deauville score [DS]). In 24/44 (55 %) patients additional comparison to ¹¹C-MET PET was available.

RESULTS

Among two radiologists, an excellent inter-observer reliability for mpWB-MRI in a total of 84 medullary lesions was observed (ICC = 1, k = 1, p <.01). 16/17 (94.1 %) MRI-classified vital lesions had a DS of 4 or 5 on either ¹⁸F-FDG-PET or ¹¹C-MET-PET. MRI-rated non-vital lesions correlated with PET-based DS ≤ 3. When results of mpWB-MRI were compared to ¹⁸F-FDG, a fair inter-observer agreement was recorded (ICC = 0.52, k = 0.53, p <.01), while for ¹¹C-MET, an excellent concordance rate was achieved (ICC = 0.81, k = 0.79, p <.01).

CONCLUSION

The proposed mpWB-MRI interpretation algorithm allowed to assess tumor activity of myeloma lesions with high inter-observer reproducibility. We observed a substantial concordance between the mpWB-MRI classification of lesions and PET assessment based on a semi-automatically calculated 5-point scoring system analogous to the Deauville scores.

The spatio-temporal evolution of multiple myeloma from baseline to relapse-refractory states

Deciphering Multiple Myeloma evolution in the whole bone marrow is key to inform curative strategies. Here, we perform spatial-longitudinal whole-exome sequencing, including 140 samples collected from 24 Multiple Myeloma patients during up to 14 years. Applying imaging-guided sampling we observe three evolutionary patterns, including relapse driven by a single-cell expansion, competing/co-existing sub-clones, and unique sub-clones at distinct locations. While we do not find the unique relapse sub-clone in the baseline focal lesion(s), we show a close phylogenetic relationship between baseline focal lesions and relapse disease, highlighting focal lesions as hotspots of tumor evolution. In patients with ≥3 focal lesions on positron-emission-tomography at diagnosis, relapse is driven by multiple distinct sub-clones, whereas in other patients, a single-cell expansion is typically seen (p < 0.01). Notably, we observe resistant sub-clones that can be hidden over years, suggesting that a prerequisite for curative therapies would be to overcome not only tumor heterogeneity but also dormancy.