Challenges and opportunities of novel imaging techniques in monoclonal plasma cell disorders: imaging “early myeloma”

Review of whole-body magnetic resonance imaging in multiple myeloma

Multiple Myeloma (MM) is a hematological malignancy affecting bone marrow, most frequently in elderly men. Imaging has a crucial role in this disease. Recently, whole-body MRI has been introduced and it has gained growing interest due to is high sensitivity and specificity in evaluating bone marrow involvement in MM. Diffusion-weighted sequences (DWI) with apparent diffusion coefficient (ADC) maps have emerged as the most sensitive technique to evaluate patients with MM, both in the pre- and post-treatment setting. Aim of this review is to provide an overview of the role and main imaging findings of whole-body MRI in MM.

The Challenging Approach to Multiple Myeloma: From Disease Diagnosis and Monitoring to Complications Management

The outcome of multiple myeloma (MM) has significantly improved in the last few decades due to several factors such as new biological discoveries allowing to better stratify disease risk, development of more effective therapies and better management of side effects related to them. However, handling all these aspects requires an interdisciplinary approach involving multiple knowledge and collaboration of different specialists. The hematologist, faced with a patient with MM, must not only choose a treatment according to patient and disease characteristics but must also know when therapy needs to be started and how to monitor it during and after treatment. Moreover, he must deal not only with organ issues related to MM such as bone disease, renal failure or neurological disease but also with adverse events, often very serious, related to novel therapies, particularly new generation immunotherapies such as CAR T cell therapy and bispecific antibodies. In this review, we provide an overview on the newer MM diagnostic and monitoring strategies and on the main side effects of MM therapies, focusing on adverse events occurring during treatment with CAR T cells and bispecific antibodies.

Development of a whole spinal MRI-based tumor burden scoring method in participants with multiple myeloma: a pilot study of prognostic significance

The aim of the study was to develop a new whole spinal MRI-based tumor burden scoring method in participants with newly diagnosed multiple myeloma (MM) and to explore its prognostic significance. We prospectively recruited participants with newly diagnosed MM; performed whole spinal MRI (sagittal FSE T1WI, sagittal IDEAL T2WI, and axial FLAIR T2WI) on them; and collected their clinical data, early treatment response, progression-free survival (PFS), and overall survival (OS). We developed a new tumor burden scoring method according to the extent of bone marrow infiltration in five MRI patterns. All participants were divided into good response and poor response groups after four treatment cycles. Univariate, multivariate analyses, and ROC were used to determine the performance of independent predictors. Thresholds for PFS and OS were calculated using X-tile, and their prognostic significance were assessed by Kaplan-Meier. The Kruskal-Wallis H test was used to compare the differences of tumor burden score between the revised International Staging System (R-ISS) stages. The new tumor burden scoring method was used in 62 participants (median score, 12; range, 0-18). The tumor burden score (OR 1.266, p = 0.002) was an independent predictor of poor response and the AUC was 0.838. Higher tumor burden scores were associated with shorter PFS (p = 0.002) and OS (p = 0.011). The tumor burden score was higher in R-ISS-III than in R-ISS-I and R-ISS-II (p = 0.016 and p = 0.006, respectively). The tumor burden score was an excellent predictor of prognosis and may serve as a supplemental marker for R-ISS.

Predicting cytogenetic risk in multiple myeloma using conventional whole-body MRI, spinal dynamic contrast-enhanced MRI, and spinal diffusion-weighted imaging

OBJECTIVES

Cytogenetic abnormalities are predictors of poor prognosis in multiple myeloma (MM). This paper aims to build and validate a multiparametric conventional and functional whole-body MRI-based prediction model for cytogenetic risk classification in newly diagnosed MM.

METHODS

Patients with newly diagnosed MM who underwent multiparametric conventional whole-body MRI, spinal dynamic contrast-enhanced (DCE-)MRI, spinal diffusion-weighted MRI (DWI) and had genetic analysis were retrospectively included (2011-2020/Ghent University Hospital/Belgium). Patients were stratified into standard versus intermediate/high cytogenetic risk groups. After segmentation, 303 MRI features were extracted. Univariate and model-based methods were evaluated for feature and model selection. Testing was performed using receiver operating characteristic (ROC) and precision-recall curves. Models comparing the performance for genetic risk classification of the entire MRI protocol and of all MRI sequences separately were evaluated, including all features. Four final models, including only the top three most predictive features, were evaluated.

RESULTS

Thirty-one patients were enrolled (mean age 66 ± 7 years, 15 men, 13 intermediate-/high-risk genetics). None of the univariate models and none of the models with all features included achieved good performance. The best performing model with only the three most predictive features and including all MRI sequences reached a ROC-area-under-the-curve of 0.80 and precision-recall-area-under-the-curve of 0.79. The highest statistical performance was reached when all three MRI sequences were combined (conventional whole-body MRI + DCE-MRI + DWI). Conventional MRI always outperformed the other sequences. DCE-MRI always outperformed DWI, except for specificity.

CONCLUSIONS

A multiparametric MRI-based model has a better performance in the noninvasive prediction of high-risk cytogenetics in newly diagnosed MM than conventional MRI alone.

CRITICAL RELEVANCE STATEMENT

An elaborate multiparametric MRI-based model performs better than conventional MRI alone for the noninvasive prediction of high-risk cytogenetics in newly diagnosed multiple myeloma; this opens opportunities to assess genetic heterogeneity thus overcoming sampling bias.

KEY POINTS

• Standard genetic techniques in multiple myeloma patients suffer from sampling bias due to tumoral heterogeneity. • Multiparametric MRI noninvasively predicts genetic risk in multiple myeloma. • Combined conventional anatomical MRI, DCE-MRI, and DWI had the highest statistical performance to predict genetic risk. • Conventional MRI alone always outperformed DCE-MRI and DWI separately to predict genetic risk. DCE-MRI alone always outperformed DWI separately, except for the parameter specificity to predict genetic risk. • This multiparametric MRI-based genetic risk prediction model opens opportunities to noninvasively assess genetic heterogeneity thereby overcoming sampling bias in predicting genetic risk in multiple myeloma.

The quantitative parameters based on marrow metabolism derived from synthetic MRI: A pilot study of prognostic value in participants with newly diagnosed multiple myeloma

BACKGROUND

The value of SyMRI-derived parameters from lumbar marrow for predicting early treatment response and optimizing the risk stratification of the Revised International Staging System (R-ISS) in participants with multiple myeloma (MM) is unknown.

METHODS

We prospectively enrolled participants with newly diagnosed MM before treatment. The SyMRI of lumbar marrow was used to calculate T1, T2, and PD values and the clinical features were collected. All participants were divided into good response (≥VGPR) and poor response (

RESULTS

Fifty-nine participants (good response, n = 33; poor response, n = 26) were evaluated. The bone marrow plasma cell percentage, β2-microglobulin, T1 and T2 value were difference between two groups (all p < 0.05). The T1 (odds ratio 1.003, p = 0.005) and T2 values (odds ratio 0.910, p = 0.002) were independent predictors and the AUC and cut-off values were 0.787, 967.2 ms and 0.784, 75.9 ms, respectively. There were no significant differences in SyMRI parameters between genders. Participants with both T1 value ≥967.2 ms and T2 value ≤75.9 ms in the R-ISS II stage were potentially to get poor response.

CONCLUSIONS

Synthetic MRI is a promising tool for predicting early treatment response to MM and promoting R-ISS II stage risk stratification.

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Key Words

• R‐ISS stage
• early treatment response
• magnetic resonance imaging
• multiple myeloma
• tumor burden

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MESH Headings

• Humans
• Male
• Female
• Prognosis
• Multiple Myeloma/diagnostic imaging
• Multiple Myeloma/pathology
• Bone Marrow/diagnostic imaging
• Bone Marrow/pathology
• Pilot Projects
• Neoplasm Staging
• Magnetic Resonance Imaging
• Retrospective Studies

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Grants

• 82071898 National Natural Science Foundation of China
• National Natural Science Foundation of China

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Affiliation(s)

Sha Cui Department of Medical ImagingShanxi Medical UniversityTaiyuanChina Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Yinnan Guo Department of PainFifth Hospital of Shanxi Medical UniversityTaiyuanChina
Weiran Niu Department of Medical ImagingShanxi Medical UniversityTaiyuanChina
Jianting Li Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Wenjin Bian Department of Medical ImagingShanxi Medical UniversityTaiyuanChina
Wenqi Wu Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Wenjia Zhang Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Qian Zheng Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Jun Wang Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina
Jinliang Niu Department of RadiologySecond Hospital of Shanxi Medical UniversityTaiyuanChina

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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.

Advances in minimal residual disease monitoring in multiple myeloma

Multiple myeloma (MM) is characterized by the clonal expansion of plasma cells and the excretion of a monoclonal immunoglobulin (M-protein), or fragments thereof. This biomarker plays a key role in the diagnosis and monitoring of MM. Although there is currently no cure for MM, novel treatment modalities such as bispecific antibodies and CAR T-cell therapies have led to substantial improvement in survival. With the introduction of several classes of effective drugs, an increasing percentage of patients achieve a complete response. This poses new challenges to traditional electrophoretic and immunochemical M-protein diagnostics because these methods lack sensitivity to monitor minimal residual disease (MRD). In 2016, the International Myeloma Working Group (IMWG) expanded their disease response criteria with bone marrow-based MRD assessment using flow cytometry or next-generation sequencing in combination with imaging-based disease monitoring of extramedullary disease. MRD status is an important independent prognostic marker and its potential as a surrogate endpoint for progression-free survival is currently being studied. In addition, numerous clinical trials are investigating the added clinical value of MRD-guided therapy decisions in individual patients. Because of these novel clinical applications, repeated MRD evaluation is becoming common practice in clinical trials as well as in the management of patients outside clinical trials. In response to this, novel mass spectrometric methods that have been developed for blood-based MRD monitoring represent attractive minimally invasive alternatives to bone marrow-based MRD evaluation. This paves the way for dynamic MRD monitoring to allow the detection of early disease relapse, which may prove to be a crucial factor in facilitating future clinical implementation of MRD-guided therapy. This review provides an overview of state-of-the-art of MRD monitoring, describes new developments and applications of blood-based MRD monitoring, and suggests future directions for its successful integration into the clinical management of MM patients.

Development of a Semiquantitative Whole-Body MRI Scoring System for Multiple Myeloma

Background In patients with multiple myeloma (MM), the serum marker β2-microglobulin does not always accurately reflect tumor load. In contrast, whole-body (WB) MRI has shown high sensitivity for detecting bone lesions. Purpose To develop and validate a semiquantitative WB MRI scoring system for newly diagnosed MM and to compare it with the International Staging System (ISS) and Revised ISS (R-ISS). Materials and Methods This study included two retrospective groups (group 1, July 2015 to September 2021; group 2, February 2020 to September 2021) and one prospective group (group 3, October 2021 to February 2022) of patients with newly diagnosed MM. A new scoring system for MM was developed using spine MRI scans in group 1 and WB MRI scans in group 2 that integrated three features: (a) background marrow pattern, (b) number of focal bone lesions, and (c) presence of extramedullary or paramedullary lesions. The summed total score ranged from zero to nine. The interobserver agreement for each feature was assessed using Fleiss or Cohen weighted κ. WB MRI total scores in group 3 were compared across ISS and R-ISS stages using two-way analysis of variance. Results Groups 1, 2, and 3 included 103 patients (mean age, 62.1 years ± 9.1 [SD]; 60 men), 36 patients (mean age 65.4 years ± 11.3 [SD]; 19 women), and 39 participants (mean age, 62.0 years ± 11.7 [SD]; 20 men), respectively. The interobserver agreements for the three features composing the scoring system were substantial (κ range, 0.69-0.80). WB MRI total score increased with increasing ISS stage (mean score for ISS 1, 2, and 3 was 2.2, 4.2, and 5.8, respectively; P = .009) and R-ISS stage (mean score for R-ISS 1, 2, and 3 was 2.1, 3.8, and 5.9, respectively; P = .005). Conclusion The developed WB MRI scoring system for MM demonstrated substantial observer agreement and corresponded well with ISS and R-ISS stages. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Dragan and Messiou in this issue.

99mTc-CD3813: A Nanobody-Based Single Photon Emission Computed Tomography Radiotracer with Clinical Potential for Myeloma Imaging and Evaluation of CD38 Expression

Daratumumab (DARA) is an anti-CD38 monoclonal antibody for the treatment of multiple myeloma (MM). The tumor CD38 expression level is one of the important factors in determining the efficacy of DARA treatment. Therefore, there is an urgent clinical need for a noninvasive tool to evaluate the CD38 levels in cancer patients before, during, and after DARA treatment. In this study, we prepared a new molecular imaging probe ^99mTc-CD3813, the ^99mTc-labeled nanobody CD3813, for noninvasive imaging of CD38 expression by single photon emission computed tomography (SPECT). We evaluated ^99mTc-CD3813 for its CD38 affinity and specificity and its capacity to image the CD38 expression in the MM and lymphoma xenografts models. ^99mTc-CD3813 SPECT/CT is able to visualize subcutaneous/orthotopic myeloma lesions in animal models and has advantages over ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography. Excess DARA has less impact on its tumor uptake (3.14 ± 0.83 vs 2.29 ± 0.91 %ID/g, n.s.), strongly suggesting that there is no competition between ^99mTc-CD3813 and DARA in binding to CD38. ^99mTc-CD3813 SPECT/CT revealed significant reduction in CD38 expression in the Ramos-bearing mice under DARA treatment, as evidenced by their reduced tumor uptake (3.04 ± 0.70 vs 1.07 ± 0.28 %ID/cc, P < 0.001). ^99mTc-CD3813 SPECT/CT was also able to detect the increased tumor uptake (0.79 ± 0.29 vs 2.12 ± 0.12 %ID/cc, P < 0.001) due to the upregulation of CD38 levels caused by all-trans retinoic acid infection. ^99mTc-CD3813 is a promising SPECT radiotracer for imaging the CD38-positive tumors and has clinical potential as a molecular imaging tool for evaluation of the CD38 expression level in patients before, during, and after DARA treatment.

Modern radiographic imaging in multiple myeloma, what is the minimum requirement?

Imaging innovations offer useful techniques applicable to many oncology specialties. Treatment advances in the field of multiple myeloma (MM) have increased the need for accurate diagnosis, particularly in the bone marrow, which is an essential component in myeloma-defining criteria. Modern imaging identifies osteolytic lesions, distinguishes solitary plasmacytoma from MM, and evaluates the presence of extramedullary disease. Furthermore, imaging is increasingly valuable in post-treatment response assessment. Detection of minimal residual disease after therapy carries prognostic implications and influences subsequent treatment planning. Whole-body low-dose Computed Tomography is now recommended over the conventional skeletal survey, and more sophisticated functional imaging methods, such as ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography , and diffusion-weighted Magnetic Resonance Imaging are proving effective in the assessment and monitoring of MM disease. This review focuses on understanding indications and advantages of these imaging modalities for diagnosing and managing myeloma.

Correlation between Whole Skeleton Dual Energy CT Calcium-Subtracted Attenuation and Bone Marrow Infiltration in Multiple Myeloma

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Quantification of whole skeleton calcium-subtracted attenuation with dual energy CT is feasible.

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Whole skeleton calcium-subtracted attenuation correlates with the degree of marrow infiltration by plasma cells on bone marrow biopsy.

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Whole skeleton calcium-subtracted attenuation provides complementary information to the detection of osteolytic bone lesions.

Objectives

Objective evaluation of the extent of skeletal marrow involvement in multiple myeloma remains a clinical gap for CT. We aimed to develop a quantitative segmentation pipeline for dual energy CT and to assess whether quantified whole skeleton calcium-subtracted attenuation values correlate with biopsy-derived bone marrow infiltration in multiple myeloma.

Methods

Consecutive prospective patients with suspected/established myeloma underwent dual source CT from the skull vertex to proximal tibia. Whole skeleton segmentation was performed for 120 kVp-equivalent images as follows: following Hounsfield unit (HU) thresholding, a Chan-Vese morphological operation was implemented to generate a whole skeleton segmentation mask. This mask was then applied to corresponding whole skeleton material decomposition calcium-subtracted maps, generating whole skeleton HU values. Associations with biopsy-derived bone marrow plasma cell infiltration percentage were assessed with Spearman’s rank correlation; significance was at 5%.

Results

21 patients (12 females; median (IQR) 67 (61, 73) years) were included; 16 patients had osteolytic bone lesions; 15 patients underwent bone marrow biopsy. Segmentation and quantification were feasible in all patients. Median (IQR) of the average skeletal calcium-subtracted attenuation was −59.9 HU (-66.3, −51.8HU). There was a positive correlation with bone marrow plasma cell infiltration percentage (Spearman’s rho: + 0.79, p < 0.001).

Conclusion

Whole skeleton calcium-subtracted attenuation is associated with the degree of bone marrow infiltration by plasma cells, providing an objective measure of marrow involvement with the potential to allow earlier detection of disease.

Imaging of treatment response and minimal residual disease in multiple myeloma: state of the art WB-MRI and PET/CT

Bone imaging has been intimately associated with the diagnosis and staging of multiple myeloma (MM) for more than 5 decades, as the presence of bone lesions indicates advanced disease and dictates treatment initiation. The methods used have been evolving, and the historical radiographic skeletal survey has been replaced by whole body CT, whole body MRI (WB-MRI) and [¹⁸F]FDG-PET/CT for the detection of bone marrow lesions and less frequent extramedullary plasmacytomas.Beyond diagnosis, imaging methods are expected to provide the clinician with evaluation of the response to treatment. Imaging techniques are consistently challenged as treatments become more and more efficient, inducing profound response, with more subtle residual disease. WB-MRI and FDG-PET/CT are the methods of choice to address these challenges, being able to assess disease progression or response and to detect "minimal" residual disease, providing key prognostic information and guiding necessary change of treatment.This paper provides an up-to-date overview of the WB-MRI and PET/CT techniques, their observations in responsive and progressive disease and their role and limitations in capturing minimal residual disease. It reviews trials assessing these techniques for response evaluation, points out the limited comparisons between both methods and highlights their complementarity with most recent molecular methods (next-generation flow cytometry, next-generation sequencing) to detect minimal residual disease. It underlines the important role of PET/MRI technology as a research tool to compare the effectiveness and complementarity of both methods to address the key clinical questions.

Whole-body magnetic resonance imaging (WBMRI) versus whole-body computed tomography (WBCT) for myeloma imaging and staging

Myeloma-associated bone disease (MBD) develops in about 80-90% of patients and severely affects their quality of life, as it accounts for the majority of mortality and morbidity. Imaging in multiple myeloma (MM) and MBD is of utmost importance in order to detect bone and bone marrow lesions as well as extraosseous soft-tissue masses and complications before the initiation of treatment. It is required for determination of the stage of disease and aids in the assessment of treatment response. Whole-body low-dose computed tomography (WBLDCT) is the key modality to establish the initial diagnosis of MM and is now recommended as reference standard procedure for the detection of lytic destruction in MBD. In contrast, whole-body magnetic resonance imaging (WBMRI) has higher sensitivity for the detection of focal and diffuse plasma cell infiltration patterns of the bone marrow and identifies them prior to osteolytic destruction. It is recommended for the evaluation of spinal and vertebral lesions, while functional, diffusion-weighted MRI (DWI-MRI) is a promising tool for the assessment of treatment response. This review addresses the current improvements and limitations of WBCT and WBMRI for diagnosis and staging in MM, underlining the fact that both modalities offer complementary information. It further summarizes the corresponding radiological findings and novel technological aspects of both modalities.

Comparative Performance of Whole Body MRI and 18F-FDG PET/CT in Evaluation of Response to Treatment of Multiple Myeloma: Meta-analysis and Systematic Review

Background: Traditional approaches for evaluating multiple myeloma (MM) treatment response have low sensitivity for residual disease. Recent studies highlight utility of whole-body MRI or FDG PET/CT in evaluating treatment response, with increasing emphasis on DWI. Objective: This systematic review was conducted to assess the diagnostic accuracy of whole-body MRI and FDG PET/CT for treatment response assessment in MM. Evidence Acquisition: Studies using whole-body MRI or FDG PET/CT to evaluate MM treatment response were identified through search of PubMed and EMBASE databases through June 30, 2021. Pooled sensitivity and specificity for detecting response were calculated by bivariate modeling. Diagnostic performance of whole-body MRI and FDG PET/CT were compared. Subgroup analyses assessed studies comparing both modalities and studies in which whole-body MRI included DWI. Evidence Synthesis: Twelve studies comprising 373 patients were included: six evaluated both modalities, four evaluated whole-body MRI only, and two evaluated FDG PET/CT only; of studies with MRI, five used DWI. Pooled sensitivity and specificity were 87% (95% CI, 75%-93%) and 57% (95% CI, 37%-76%) for whole-body MRI, versus 64% (95% CI, 45%-79%) and 82% (95% CI, 75%-88%) for FDG PET/CT (sensitivity: p = .29; specificity: p = .01). For studies directly comparing the modalities, pooled sensitivity and specificity were 90% (95% CI, 80%-100%) and 56% (95% CI, 44%-68%) for whole-body MRI, versus 66% (95% CI, 47%-85%) and 81% (95% CI, 72%-90%) for FDG PET/CT (sensitivity: p = .18; specificity: p < .001). Sensitivity and specificity were 93% (95% CI, 75%-98%) and 57% (95% CI, 21%-87%) for DWI, versus 74% (95% CI, 60%-85%) and 56% (95% CI, 38%-73%) for whole-body MRI without DWI (sensitivity: p = .27; specificity: p = .99). AUC was 0.84 for whole-body MRI, 0.83 for FDG PET/CT, and 0.92 for DWI. Conclusion: FDG PET/CT had significantly higher specificity, whereas whole-body MRI had higher sensitivity (though non-significant). DWI may contribute to the high sensitivity of whole-body MRI. Clinical Impact: This meta-analysis suggests potential complementary roles of whole-body MRI and FDG PET/CT in MM treatment response assessment. Future studies should explore their combination through PET/MRI.

Diagnostic Value of Whole-Body MRI Short Protocols in Bone Lesion Detection in Multiple Myeloma Patients

The aim of the study is to evaluate the effectiveness of short whole-body magnetic resonance imaging (WBMRI) protocols for the overall assessment of bone marrow involvement in patients with multiple myeloma (MM), in comparison with standard whole-body MRI protocol. Patients with biopsy-proven MM, who underwent a WBMRI with full-body coverage (from vertex to feet) were retrospectively enrolled. WBMRI images were independently evaluated by two expert radiologists, in terms of infiltration patterns (normal, focal, diffuse, and combined), according to location (the whole skeleton was divided into six anatomic districts: skull, spine, sternum and ribs, upper limbs, pelvis and proximal two-thirds of the femur, remaining parts of lower limbs) and lytic lesions number (<5, 5-20, and >20). The majority of patients showed focal and combined infiltration patterns with bone lesions predominantly distributed in the spine and pelvis. As skull and lower limbs are less frequently involved by focal bone lesions, excluding them from the standard MRI protocol allows to obtain a shorter protocol, maintaining a good diagnostic value.

Updates and Ongoing Challenges in Imaging of Multiple Myeloma: AJR Expert Panel Narrative Review

Advances in the understanding and treatment of multiple myeloma have led to the need for more sensitive and accurate imaging of intramedullary and extramedullary disease. This role of imaging is underscored by recently revised imaging recommendations of the International Myeloma Working Group (IMWG). This narrative review discusses these recommendations from the IMWG for different disease stages, focusing on advanced whole-body modalities, and addresses related challenges and controversies. In the recommendations, whole-body low-dose CT is central in initial patient assessment, replacing the conventional skeletal survey. Although the recommendations favor MRI for diagnosis because of its superior sensitivity and utility in identifying myeloma-defining events, FDG PET/CT is recommended as the modality of choice for assessing treatment response. Consensus opinions are offered regarding the role of imaging in multiple myeloma for characterization of disease distribution, determination of prognosis, and response evaluation.

Whole Body Low Dose Computed Tomography (WBLDCT) Can Be Comparable to Whole-Body Magnetic Resonance Imaging (WBMRI) in the Assessment of Multiple Myeloma

Aim of the study is to compare the agreement between whole-body low-dose computed tomography (WBLDCT) and magnetic resonance imaging (WBMRI) in the evaluation of bone marrow involvement in patients with multiple myeloma (MM). Patients with biopsy-proven MM, who underwent both WBLDCT and WBMRI were retrospectively enrolled. After identifying the presence of focal bone involvement (focal infiltration pattern), the whole skeleton was divided into five anatomic districts (skull, spine, sternum and ribs, pelvis, and limbs). Patients were grouped according to the number and location of the lytic lesions (<5, 5-20, and >20) and Durie and Salmon staging system. The agreement between CT and MRI regarding focal pattern, staging, lesion number, and distribution was assessed using the Cohen Kappa statistics. The majority of patients showed focal involvement. According to the distribution of the focal lesions and Durie Salmon staging, the agreement between CT and MRI was substantial or almost perfect (all κ > 0.60). The agreement increased proportionally with the number of lesions in the pelvis and spine (κ = 0.373 to κ = 0.564, and κ = 0.469-0.624), while for the skull the agreement proportionally decreased without reaching a statistically significant difference (p > 0.05). In conclusion, WBLDCT showed an almost perfect agreement in the evaluation of focal involvement, staging, lesion number, and distribution of bone involvement in comparison with WBMRI.

Comparison of [18F]FDG PET/CT and MRI for Treatment Response Assessment in Multiple Myeloma: A Meta-Analysis

The present study was designed to assess the additional value of 2-deoxy-2[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) to magnetic resonance imaging (MRI) in the treatment response assessment of multiple myeloma (MM). We performed a meta-analysis of all available studies to compare the detectability of treatment response of [¹⁸F]FDG PET/CT and MRI in treated MM. We defined detecting a good therapeutic effect as positive, and residual disease as negative. We determined the sensitivities and specificities across studies, calculated the positive and negative likelihood ratios (LR), and made summary receiver operating characteristic curves (SROC) using hierarchical regression models. The pooled analysis included six studies that comprised 278 patients. The respective performance characteristics (95% confidence interval (CI)) of [¹⁸F]FDG PET/CT and MRI were as follows: sensitivity of 80% (56% to 94%) and 25% (19% to 31%); specificity of 58% (44% to 71%) and 83% (71% to 91%); diagnostic odds ratio (DOR) of 6.0 (3.0-12.0) and 1.7 (0.7-2.7); positive LR of 1.8 (1.3-2.4) and 1.4 (0.7-2.7); and negative LR of 0.33 (0.21-0.53) and 0.81 (0.62-1.1). In the respective SROC curves, the area under the curve was 0.77 (SE, 0.038) and 0.59 (SE, 0.079) and the Q* index was 0.71 and 0.57. Compared with MRI, [¹⁸F]FDG PET/CT had higher sensitivity and better DOR and SROC curves. Compared with MRI, [¹⁸F]FDG PET/CT had greater ability to detect the treatment assessment of MM.

Defining the undetectable: The current landscape of minimal residual disease assessment in multiple myeloma and goals for future clarity

Multiple Myeloma, the second most prevalent hematologic malignancy, yet lacks an established curative therapy. However, overall response rate to modern four-drug regimens approaches 100%. Major efforts have thus focused on the measurement of minute quantities of residual disease (minimal residual disease or MRD) for prognostic metrics and therapeutic response evaluation. Currently, MRD is assessed by flow cytometry or by next generation sequencing to track tumor-specific immunoglobulin V(D)J rearrangements. These bone marrow-based methods can reach sensitivity thresholds of the identification of one neoplastic cell in 1,000,000 (10-6). New technologies are being developed to be used alone or in conjunction with established methods, including peripheral blood-based assays, mass spectrometry, and targeted imaging. Data is also building for MRD as a surrogate endpoint for overall survival. Here, we will address the currently utilized MRD assays, challenges in validation across labs and clinical trials, techniques in development, and future directions for successful clinical application of MRD in multiple myeloma.

F-18 FDG PET/CT and F-18 FLT PET/CT as predictors of outcome in patients with multiple myeloma. A pilot study

OBJECTIVES

We evaluated the prognostic significance of the combined use of F-18 FDG (FDG) and F-18 FLT (FLT) PET/CT (PET/CT) in patients (pts) with multiple myeloma (MM) suspected relapse after a first line chemotherapy.

METHODS

twenty-eight patients (57 ± 12 years) underwent both PET/CT scans over 2-4 weeks. Patients were grouped according to imaging results (FDG+/-; FLT+/-) and the findings compared to the event free survival (EFS).

RESULTS

five pts had FDG+; FLT+, 8 showed FDG+;FLT-, two had FDG-;FLT + and 13 presented FDG-;FLT-, mostly (87 %) of FDG+;FLT- pts had destructive lytic bone lesions. At Cox regression analysis the FDG PET/CT (HR 4.4, 95 % CI 1.3-15.4, p < 0.05) and FLT PET/CT (HR 5.8, 95 % CI 1.7-19.3, p < 0.01) were predictive of worst prognosis. The Kaplan-Meier analysis showed that FDG and FLT PET/CT independently influenced the survival. FDG-;FLT-patients had better EFS as compared to FDG+; FLT + pts and FDG-;FLT + pts, those of FDG+;FLT- group also had worsened EFS.

CONCLUSIONS

results from the aggregate use of PET/CT FDG and FLT in MM represent a valuable prognostic indicator for identifying patients at higher risk of undue events and may help to correctly stratify the patients with suspected relapse.

Whole-Body Functional MRI and PET/MRI in Multiple Myeloma

Simple Summary

Whole-body magnetic resonance imaging (MRI) is recognized as the most sensitive imaging technique for the detection of bone marrow infiltration, and was therefore, recently included in the new diagnostic myeloma criteria, as proposed by the International Myeloma Working Group. The use of diffusion-weighted MRI further improved the performances of whole-body MRI in the setting of multiple myeloma, and its systematic implementation in general clinical practice is now recommended. Whole-body, dynamic, contrast-enhanced MRI might provide further information on lesions vascularity and might help evaluate response to treatment. Hybrid PET/MRI might act as the optimal imaging modality, owing to the association of the best techniques for both detecting bone marrow involvement and evaluating treatment response, providing one-stop-shop imaging in a whole-body scale. This review provides an overview on the value of whole-body MRI, including diffusion-weighted and dynamic contrast-enhanced MRI and whole-body ¹⁸F-FDG PET/MRI in diagnosis, staging, and response evaluation in multiple myeloma.

Abstract

Bone disease is one of the major features of multiple myeloma (MM), and imaging has a pivotal role in both diagnosis and follow-up. Whole-body magnetic resonance imaging (MRI) is recognized as the gold standard for the detection of bone marrow involvement, owing to its high sensitivity. The use of functional MRI sequences further improved the performances of whole-body MRI in the setting of MM. Whole-body diffusion-weighted (DW) MRI is the most attractive functional technique and its systematic implementation in general clinical practice is now recommended by the International Myeloma Working Group. Whole-body dynamic contrast-enhanced (DCE) MRI might provide further information on lesions vascularity and help evaluate response to treatment. Whole Body PET/MRI is an emerging hybrid imaging technique that offers the opportunity to combine information on morphology, fat content of bone marrow, bone marrow cellularity and vascularization, and metabolic activity. Whole-body PET/MRI allows a one-stop-shop examination, including the most sensitive technique for detecting bone marrow involvement, and the most recognized technique for treatment response evaluation. This review aims at providing an overview on the value of whole-body MRI, including DW and DCE MRI, and combined whole-body ¹⁸F-FDG PET/MRI in diagnosis, staging, and response evaluation in patients with MM.

CD38-targeted Immuno-PET of Multiple Myeloma: From Xenograft Models to First-in-Human Imaging

Background Current measurements of multiple myeloma disease burden are suboptimal. Daratumumab is a monoclonal antibody that targets CD38, an antigen expressed on nearly all myeloma cells. Purpose To demonstrate preclinical and first-in-human application of an antibody composed of the native daratumumab labeled with the positron-emitting radionuclide zirconium 89 (⁸⁹Zr) through the chelator deferoxamine (DFO), or ⁸⁹Zr-DFO-daratumumab, for immunologic PET imaging of multiple myeloma. Materials and Methods ⁸⁹Zr-DFO-daratumumab was synthesized by conjugating ⁸⁹Zr to daratumumab with DFO. A murine xenograft model using CD38-positive OPM2 multiple myeloma cells was used to evaluate CD38-specificity of ⁸⁹Zr-DFO-daratumumab. Following successful preclinical imaging, a prospective phase I study of 10 patients with multiple myeloma was performed. Study participants received 74 MBq (2 mCi) of intravenous ⁸⁹Zr-DFO-daratumumab. Each participant underwent four PET/CT scans over the next 8 days, as well as blood chemistry and whole-body counts, to determine safety, tracer biodistribution, pharmacokinetics, and radiation dosimetry. Because ⁸⁹Zr has a half-life of 78 hours, only a single administration of tracer was needed to obtain all four PET/CT scans. Results ⁸⁹Zr-DFO-daratumumab was synthesized with radiochemical purity greater than 99%. In the murine model, substantial bone marrow uptake was seen in OPM2 mice but not in healthy mice, consistent with CD38-targeted imaging of OPM2 multiple myeloma cells. In humans, ⁸⁹Zr-DFO-daratumumab was safe and demonstrated acceptable dosimetry. ⁸⁹Zr-DFO-daratumumab uptake was visualized at PET in sites of osseous myeloma. Conclusion These data demonstrate successful CD38-targeted immunologic PET imaging of multiple myeloma in a murine model and in humans. © RSNA, 2020 Online supplemental material is available for this article.

Determination of Minimal Residual Disease in Multiple Myeloma: Does It Matter?

PURPOSE OF REVIEW

The ability to detect minimal residual disease (MRD) in myeloma has improved due to advances in flow cytometry and sequencing methodologies. Here, we evaluate recent clinical trial data and explore the current and future roles of MRD assessment in the context of clinical trial design and clinical practice.

RECENT FINDINGS

A review of recent phase III studies reveals that achievement of MRD negativity is associated with improved progression-free survival (PFS) and/or overall survival (OS). Treatment arms that are more effective from a PFS or overall response rate perspective are also associated with superior MRD negativity rates. The current standard MRD methodologies are limited by requiring bone marrow samples and refinement of methodologies that can detect disease outside of the bone marrow is needed. Currently, MRD is a prognostic biomarker and further efforts are required to determine whether it can serve as a surrogate endpoint. The use of MRD status to guide treatment decisions is currently not recommended outside the confines of a clinical trial.

Tumor load in patients with multiple myeloma: β₂-microglobulin levels versus low-dose whole-body CT

OBJECTIVE

Beta-2-microglobulin is a serum marker of tumor burden in multiple myeloma (MM). Our aim was to correlate serum β₂-microglobulin levels in patients with MM to tumor burden determined by low-dose whole-body CT (LDWBCT).

MATERIALS AND METHODS

A total of 52 patients with newly diagnosed, untreated MM who underwent LDWBCT were included. LDWBCT scans were assessed by two musculoskeletal radiologists in consensus for focal lesions. The Durie and Salmon PLUS staging system was used for staging patients in stages I-III. β₂-microglobulin was also subdivided into stages I-III on the basis of the multiple myeloma International Staging System (ISS).

RESULTS

Using the Durie and Salmon PLUS staging system criteria for image evaluation, we were able to identify stage I MM in 17 patients, stage II MM in nine patients, and stage III MM in 26 patients. Eight of nine patients with stage II MM and 16 of 26 patients with stage III MM had normal β₂-microglobulin levels. Thus, 24 of 35 patients (68.6%) had 5 or more focal lesions and false-negative β₂-microglobulin levels.

CONCLUSION

Serum β₂-microglobulin levels alone may not indicate the full extent of tumor burden in a significant subset of myeloma patients.

Clinical Applications and Future Directions of Minimal Residual Disease Testing in Multiple Myeloma

In the last years, the life expectancy of multiple myeloma (MM) patients has substantially improved thanks to the availability of many new drugs. Our ability to induce deep responses has improved as well, and the treatment goal in patients tolerating treatment moved from the delay of progression to the induction of the deepest possible response. As a result of these advances, a great scientific effort has been made to redefine response monitoring, resulting in the development and validation of high-sensitivity techniques to detect minimal residual disease (MRD). In 2016, the International Myeloma Working Group (IMWG) updated MM response categories defining MRD-negative responses both in the bone marrow (assessed by next-generation flow cytometry or next-generation sequencing) and outside the bone marrow. MRD is an important factor independently predicting prognosis during MM treatment. Moreover, using novel combination therapies, MRD-negative status can be achieved in a fairly high percentage of patients. However, many questions regarding the clinical use of MRD status remain unanswered. MRD monitoring can guide treatment intensity, although well-designed clinical trials are needed to demonstrate this potential. This mini-review will focus on currently available techniques and data on MRD testing and their potential future applications.

Current and potential applications of positron emission tomography for multiple myeloma and plasma cell disorders

Fluorine-18 (18F)-fluorodeoxyglucose (FDG) positron emission tomography (PET) allows evaluation of elevated glucose metabolism in malignancies. There has been increasing interest in FDG PET/CT for plasma cell disorders since the International Myeloma Working Group outlined multiple applications of this imaging modality, including distinguishing smoldering myeloma from active multiple myeloma, confirmation of solitary plasmacytoma, and multiple indications in patients with known multiple myeloma, including determining extent of initial disease, monitoring therapy response, and detection of residual disease following therapy. The field of molecular imaging is now shifting focus from evaluation of metabolism to targeted evaluation of specific tumor markers. Targeted PET imaging targeted of CXCR4 and CD38 has advanced into translational clinical trials, bringing us closer to powerful imaging options for myeloma. In this review we discuss the current applications of FDG PET/CT in plasma cell disorders, as well as advances in targeted PET imaging.

Antibody-targeting of ultra-small nanoparticles enhances imaging sensitivity and enables longitudinal tracking of multiple myeloma

Monitoring malignant progression and disease recurrence post-therapy are central challenges to improving the outcomes of patients with multiple myeloma (MM). Whereas current detection methods that rely upon bone marrow examination allow for precise monitoring of minimal residual disease and can help to elucidate clonal evolution, they do not take into account the spatial heterogeneity of the tumor microenvironment. As such, they are uninformative as to the localization of malignant plasma cells and may lead to false negative results. With respect to the latter challenge, clinically-available imaging agents are neither sufficiently sensitive nor specific enough to detect minute plasma cell populations. Here, we sought to explore methods by which to improve detection of MM cells within their natural bone marrow environment, using whole-animal magnetic resonance imaging to longitudinally monitor early-stage disease as well as to enhance tumor detection after systemic therapy. We conducted a proof-of-concept study to demonstrate that ultra-small (<5 nm) gadolinium-containing nanoparticles bound to full-length antibodies against the B-cell maturation antigen (BCMA) exhibit rapid tumor uptake followed by renal clearance, improving the signal-to-noise ratio for MM detection beyond levels that are currently afforded by other FDA-approved clinical imaging modalities. We anticipate that when combined with bone marrow or blood biopsy, such imaging constructs could help to augment the effective management of patients with MM.

[PET/CT with 18F-fluorodeoxyglucose and 11C-methionine after autologous stem cell transplantation in multiple myeloma patients]

AIM

to compare the results of tumor visualization when using 18F-FDG and 11C-methionine PET/CT after auto-HSCT in MM patients.

MATERIALS AND METHODS

A prospective study included 27 MM patients subjected to 18F-FDG and 11C-methionine PET/CT on day 100 after auto-HSCT. Obtained images were visually and semi - quantitatively analyzed. Focal areas of increased uptake for every radiopharmaceutical agent (hypermetabolic foci) not associated with its physiological distribution were registered. Maximum Standardized Uptake Values (SUVmax) in pathological foci were automatically calculated for every radiopharmaceutical agent separately. PET/CT findings were compared to antitumor response achieved after auto-HSCT according to International MM Working Group criteria.

RESULTS

After auto-HSCT, the majority of patients (16/60%) achieved a complete response. Abnormal 18F-FDG uptake was registered in 37% (n=10) of patients, negative PET findings were obtained in 63% (n=17) of patients. 11C-methionine PET/CT revealed hypermetabolic foci in 67% (n=18) of patients, and there was no 11C-methionine uptake in 33% (n=9). Pathological foci of radiopharmaceutical agent uptake were 1.8 times more frequently revealed using PET/CT with 11C-methionine (p.

Guidelines for Acquisition, Interpretation, and Reporting of Whole-Body MRI in Myeloma: Myeloma Response Assessment and Diagnosis System (MY-RADS)

Acknowledging the increasingly important role of whole-body MRI for directing patient care in myeloma, a multidisciplinary, international, and expert panel of radiologists, medical physicists, and hematologists with specific expertise in whole-body MRI in myeloma convened to discuss the technical performance standards, merits, and limitations of currently available imaging methods. Following guidance from the International Myeloma Working Group and the National Institute for Clinical Excellence in the United Kingdom, the Myeloma Response Assessment and Diagnosis System (or MY-RADS) imaging recommendations are designed to promote standardization and diminish variations in the acquisition, interpretation, and reporting of whole-body MRI in myeloma and allow response assessment. This consensus proposes a core clinical protocol for whole-body MRI and an extended protocol for advanced assessments. Published under a CC BY 4.0 license. Online supplemental material is available for this article.

Discriminating Depth of Response to Therapy in Multiple Myeloma Using Whole-body Diffusion-weighted MRI with Apparent Diffusion Coefficient: Preliminary Results From a Single-center Study

RATIONALE AND OBJECTIVES

This study aimed to measure apparent diffusion coefficient (ADC) in Chinese patients with newly diagnosed multiple myeloma by whole-body diffusion-weighted magnetic resonance imaging (WB-DWI MRI) and assess the diagnostic accuracy of ADC in the discrimination of deep response to induction chemotherapy.

MATERIALS AND METHODS

Seventeen patients underwent WB-DWI MRI before and after induction chemotherapy (week 20). DWI images and ADC maps were produced and 89 regions of interest were chosen. ADC percent changes were compared between deep (complete response or very good partial response) and non-deep responders (partial response, minimal response, stable disease, or progressive disease) as International Myeloma Working Group criteria. Diagnostic accuracy of ADC was calculated using specific cut offs. Predictive positive value of ADC was calculated to predict deep response to consolidation therapy.

RESULTS

Lesions reduced in size and number and signal intensity decreased in follow-up DWI, which did not differ between deep and non-deep responders. ADC percent changes were significantly higher in deep responders (36.79%) than in non-deep responders (11.50%) after induction therapy (P = .02) in per lesion analysis. ADC percent increases by 46.96%, 78.0% yielded specificity at 81.4%, 90.7% in discriminating deep response to induction therapy. Predictive positive value predicting deep response to consolidation therapy was 60.5% by using ADC cutoff >1.00 × 10^-3 mm²/s at week 20.

CONCLUSIONS

ADC from WB-DWI MRI increased remarkably in patients who achieved deep response at the end of induction chemotherapy, which represented a confirmatory diagnostic tool to discriminate deep response to induction therapy for patients with multiple myeloma. ADC may have a potential to predict deep response to consolidation therapy.

Current concepts in tumor imaging with whole-body MRI with diffusion imaging (WB-MRI-DWI) in multiple myeloma and lymphoma

Whole-body MRI (WB-MRI) with diffusion-weighted imaging (DWI) can now be used to stage and restage multiple myeloma (MM) and lymphoma. Magnetic resonance imaging (MRI) is the standard tool to detect BM involvement (BMI). The 2016 diagnostic criteria of the International Myeloma Working Group identify WB-MRI and fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) as the most sensitive imaging techniques for detecting skeletal and extra-skeletal MM invasion, respectively. Preliminary findings have also shown that WB-MRI is better than CT and equal to PET/CT in staging aggressive lymphoma and Hodgkin lymphoma, whereas MRI is better for diagnosing BMI in patients with low-grade lymphoma. Signal intensity (SI) and the apparent diffusion coefficient (ADC) are useful metrics to quantify the chemotherapy response in WB-MRI.

Minimal residual disease in multiple myeloma: use of magnetic resonance imaging

The increasing percentage of patients achieving deep responses in multiple myeloma has led to the need for more sophisticated instruments to measure residual disease as a potential source of relapse. As minimal residual disease assessment is mostly performed on a bone marrow specimen from a certain area of the body, such samples have the limitation that they might not really represent the actual tumor burden, because focal accumulations of malignant cells might be either hit or missed. Magnetic resonance imaging is a highly sensitive technique for the assessment of tumor burden and can be performed as whole-body protocol, overcoming the problem of sampling error for minimal residual disease assessment. Despite its high sensitivity, however, magnetic resonance imaging cannot differentiate between vital and necrotic lesions after therapy. Therefore, new fusion and functional techniques are currently under investigation, and image-guided biopsies are performed to combine the strengths of all available methods.

Body fat composition as predictive factor for treatment response in patients with newly diagnosed multiple myeloma - subgroup analysis of the prospective GMMG MM5 trial

INTRODUCTION/BACKGROUND

Obesity is a well-known risk factor for malignant tumors and increased body mass index (BMI) is correlated to the risk of developing multiple myeloma (MM). The correlation of body fat composition with disease activity, adverse events and treatment response of MM patients has not been investigated yet.

PATIENTS AND METHODS

A subgroup of 108 patients from a single institution enrolled in the prospective GMMG-MM5 trial, who received a whole-body low-dose computed tomography (WBLDCT) before induction therapy, were included in this study. Body fat composition was measured in WBLDCT for each patient, divided in the compartments abdomen, pelvis, thigh and further categorized in subcutaneous (SAT) and visceral adipose tissue (VAT). The correlation of these parameters with disease activity (M protein, plasma cell count, LDH, CRAB-criteria), adverse cytogenetics, adverse events and treatment response were evaluated.

RESULTS

Significant reciprocal correlation was found between adverse cytogenetics and VAT of the abdomen and pelvis, respectively (gain 1q21: p=0.009 and p=0.021; t(4;14): p=0.038 and p=0.042). No correlation of VAT or SAT with adverse events was observed. Significant reciprocal correlation was observed between abdominal (p=0.03) and pelvic (p=0.035) VAT and treatment response. Abdominal VAT remains significant (p=0.034) independently of revised ISS stage and treatment. The BMI did not show a significant correlation with treatment response or investigated cytogenetics.

CONCLUSION

Based on the clinically relevant difference in treatment outcome depending on VAT and SAT, excessive body fat of abdomen and pelvis might be a predictive factor for poor treatment response. Further influences in this context should be considered as well, e.g. chemotherapy dosing and body fat metabolism. Further studies are necessary to investigate this hypothesis.

International Myeloma Working Group consensus criteria for response and minimal residual disease assessment in multiple myeloma

Treatment of multiple myeloma has substantially changed over the past decade with the introduction of several classes of new effective drugs that have greatly improved the rates and depth of response. Response criteria in multiple myeloma were developed to use serum and urine assessment of monoclonal proteins and bone marrow assessment (which is relatively insensitive). Given the high rates of complete response seen in patients with multiple myeloma with new treatment approaches, new response categories need to be defined that can identify responses that are deeper than those conventionally defined as complete response. Recent attempts have focused on the identification of residual tumour cells in the bone marrow using flow cytometry or gene sequencing. Furthermore, sensitive imaging techniques can be used to detect the presence of residual disease outside of the bone marrow. Combining these new methods, the International Myeloma Working Group has defined new response categories of minimal residual disease negativity, with or without imaging-based absence of extramedullary disease, to allow uniform reporting within and outside clinical trials. In this Review, we clarify several aspects of disease response assessment, along with endpoints for clinical trials, and highlight future directions for disease response assessments.

Quantitative MRI and spectroscopy of bone marrow

Bone marrow is one of the largest organs in the human body, enclosing adipocytes, hematopoietic stem cells, which are responsible for blood cell production, and mesenchymal stem cells, which are responsible for the production of adipocytes and bone cells. Magnetic resonance imaging (MRI) is the ideal imaging modality to monitor bone marrow changes in healthy and pathological states, thanks to its inherent rich soft‐tissue contrast. Quantitative bone marrow MRI and magnetic resonance spectroscopy (MRS) techniques have been also developed in order to quantify changes in bone marrow water–fat composition, cellularity and perfusion in different pathologies, and to assist in understanding the role of bone marrow in the pathophysiology of systemic diseases (e.g. osteoporosis). The present review summarizes a large selection of studies published until March 2017 in proton‐based quantitative MRI and MRS of bone marrow. Some basic knowledge about bone marrow anatomy and physiology is first reviewed. The most important technical aspects of quantitative MR methods measuring bone marrow water–fat composition, fatty acid composition, perfusion, and diffusion are then described. Finally, previous MR studies are reviewed on the application of quantitative MR techniques in both healthy aging and diseased bone marrow affected by osteoporosis, fractures, metabolic diseases, multiple myeloma, and bone metastases.

Level of Evidence: 3

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2018;47:332–353.

Whole-body MRI, dynamic contrast-enhanced MRI, and diffusion-weighted imaging for the staging of multiple myeloma

Magnetic resonance imaging (MRI) is the most sensitive imaging technique for the detection of bone marrow infiltration, and has therefore recently been included in the new diagnostic myeloma criteria, as proposed by the International Myeloma Working Group. Nevertheless, conventional MRI only provides anatomical information and is therefore only of limited use in the response assessment of patients with multiple myeloma. The additional information from functional MRI techniques, such as diffusion-weighted imaging and dynamic contrast-enhanced MRI, can improve the detection rate of bone marrow infiltration and the assessment of response. This can further enhance the sensitivity and specificity of MRI in the staging of multiple myeloma patients. This article provides an overview of the technical aspects of conventional and functional MRI techniques with practical recommendations. It reviews the diagnostic performance, prognostic value, and role in therapy assessment in multiple myeloma and its precursor stages.

Imaging of Multiple Myeloma

Multiple myeloma is the most common bone malignancy. Imaging plays an important role in identifying the extent of the disease, disease process, guiding biopsies, and diagnosing associated spinal and intracranial complications. Multiple myeloma and related plasma cell proliferative disorders have a diverse set of clinicopathologic findings and on neuroimaging present unique and diverse findings from the disease and from complications of the disease and treatment, which are valuable for clinicians and radiologists.

Low expression of hexokinase-2 is associated with false-negative FDG-positron emission tomography in multiple myeloma

¹⁸F-Fluorodeoxyglucose (FDG)-positron emission tomography (PET) and diffusion-weighted magnetic resonance imaging with background signal suppression (DWIBS) are 2 powerful functional imaging modalities in the evaluation of malignant plasma cell (PC) disease multiple myeloma (MM). Preliminary observations have suggested that MM patients with extensive disease according to DWIBS may be reported as being disease-free on FDG-PET ("PET false-negative"). The aim of this study was to describe the proportion of PET false-negativity in a representative set of 227 newly diagnosed MM patients with simultaneous assessment of FDG-PET and DWIBS, and to identify tumor-intrinsic features associated with this pattern. We found the incidence of PET false-negativity to be 11%. Neither tumor load-associated parameters, such as degree of bone marrow PC infiltration, nor the PC proliferation rate were associated with this subset. However, the gene coding for hexokinase-2, which catalyzes the first step of glycolysis, was significantly lower expressed in PET false-negative cases (5.3-fold change, P < .001) which provides a mechanistic explanation for this feature. In conclusion, we demonstrate a relevant number of patients with FDG-PET false-negative MM and a strong association between hexokinase-2 expression and this negativity: a finding which may also be relevant for clinical imaging of other hematological cancers.

New Developments in Diagnosis, Prognosis, and Assessment of Response in Multiple Myeloma

Over the past few years, the management of multiple myeloma has changed. We have new guidelines regarding how to set the diagnosis, when to initiate therapy, and how to monitor treatment response. In 2014, the updated International Myeloma Working Group (IMWG) diagnostic criteria changed the definition of multiple myeloma from being a disease defined by symptoms to a disease defined by biomarkers. Today, modern combination therapies have reported up to 60% to 80% of patients reaching a complete response. As a logical and necessary step forward, investigators have explored strategies to detect minimal residual disease (MRD) and its correlation with clinical outcomes. Recent meta-analysis data show that MRD negativity is associated with longer progression-free survival and overall survival. In 2016, the updated IMWG response criteria include MRD as the deepest level of treatment response in multiple myeloma. Simultaneously, we are still quite behind in our understanding of the heterogeneous biology of multiple myeloma and its implications for therapy. Emerging DNA sequencing data show that newly diagnosed multiple myeloma patients have a broad range of mutations, which are distributed unevenly in multiple parallel subclones already present at diagnosis. To move beyond the ill-defined category of "high-risk multiple myeloma," which confers to approximately 25% of all newly diagnosed patients, prospective studies are needed to dissect tumor biology and define multiple myeloma subtypes, and, based on biology, seek to define rational therapies for individual subtypes. This article discusses novel insights and gives perspectives on diagnosis and MRD monitoring and future directions for prognosis and clinical management of multiple myeloma. Clin Cancer Res; 22(22); 5428-33. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "MULTIPLE MYELOMA MULTIPLYING THERAPIES".

MRI in multiple myeloma: a pictorial review of diagnostic and post-treatment findings

Magnetic resonance imaging (MRI) is increasingly being used in the diagnostic work-up of patients with multiple myeloma. Since 2014, MRI findings are included in the new diagnostic criteria proposed by the International Myeloma Working Group. Patients with smouldering myeloma presenting with more than one unequivocal focal lesion in the bone marrow on MRI are considered having symptomatic myeloma requiring treatment, regardless of the presence of lytic bone lesions. However, bone marrow evaluation with MRI offers more than only morphological information regarding the detection of focal lesions in patients with MM. The overall performance of MRI is enhanced by applying dynamic contrast-enhanced MRI and diffusion weighted imaging sequences, providing additional functional information on bone marrow vascularization and cellularity.

This pictorial review provides an overview of the most important imaging findings in patients with monoclonal gammopathy of undetermined significance, smouldering myeloma and multiple myeloma, by performing a ‘total’ MRI investigation with implications for the diagnosis, staging and response assessment.

Main message

• Conventional MRI diagnoses multiple myeloma by assessing the infiltration pattern.

• Dynamic contrast-enhanced MRI diagnoses multiple myeloma by assessing vascularization and perfusion.

• Diffusion weighted imaging evaluates bone marrow composition and cellularity in multiple myeloma.

• Combined morphological and functional MRI provides optimal bone marrow assessment for staging.

• Combined morphological and functional MRI is of considerable value in treatment follow-up.