PURPOSE: ¹⁸F-Fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is currently the standard technique to define minimal residual disease (MRD) status outside the bone marrow (BM) in patients with multiple myeloma (MM). This study aimed to define criteria for PET complete metabolic response after therapy, jointly analyzing a subgroup of newly diagnosed transplantation-eligible patients with MM enrolled in two independent European randomized phase III trials (IFM/DFCI2009 and EMN02/HO95). PATIENTS AND METHODS: Two hundred twenty-eight patients were observed for a median of 62.9 months. By study design, PET/CT scans were performed at baseline and before starting maintenance (premaintenance [PM]). The five-point Deauville scale (DS) was applied to describe BM (BM score [BMS]) and focal lesion (FL; FL score [FS]) uptake and tested a posteriori in uni- and multivariable analyses for their impact on clinical outcomes. RESULTS: At baseline, 78% of patients had FLs (11% extramedullary), 80% with an FS ≥ 4. All patients had BM diffuse uptake (35.5% with BMS ≥ 4). At PM, 31% of patients had visually detectable FLs (2% extramedullary), 24% and 67.7% of them with an FS of 3 and ≥ 4, respectively. At PM, 98% of patients retained residual BM diffuse uptake, which was significantly lower than at baseline (mainly between BMS 2 and 3, BMS was ≥ 4 in only 8.7% of patients). By both uni- and multivariable analysis, FS and BMS < 4 were associated with prolonged progression-free survival (PFS) and overall survival (OS) at PM (OS: hazard ratio [HR], 0.6 and 0.47, respectively; PFS: HR, 0.36 and 0.24, respectively) CONCLUSION: FL and BM FDG uptake lower than the liver background after therapy was an independent predictor for improved PFS and OS and can be proposed as the standardized criterion of PET complete metabolic response, confirming the value of the DS for patients with MM.

Survival of multiple myeloma (MM) has significantly improved over the past decade; however, a composed group of patients (15% to 20%), named high-risk (HR) MM, still experiences reduced survival. Both tumor biology and suboptimal/absent responses to therapy may underlie HR definition and a clear uniform identification of risk factors is crucial for proper management of these patients. In biologic HRMM, MRD attaining and sustaining negativity, inside and outside bone marrow, should be the primary goal and therapy should be adapted in patients with frailty to reduce toxicity and improve quality of life. MM treatment has traditionally been tailored to age and more recently frailty or comorbidities, but very rarely to the biology of the disease, mainly because of the lack of a clear benefit derived from a specific drug/combination, inhomogeneity in HR definition, and lack of data coming from prospective, properly designed clinical trials. Some attempts have been successfully made in this direction. In this review, we discuss the current definitions of HR and the need for a consensus, the results of available trials in HR patients, and the way through risk-adapted treatment strategies. For this purpose, we propose several clinical cases of difficult-to-treat patients throughout different treatment phases.

The International Myeloma Working Group (IMWG) recently introduced the evaluation of minimal residual disease (MRD) within the multiple myeloma (MM) response criteria, and MRD negativity assessed inside and outside the bone marrow is currently considered the most powerful predictor of favorable long-term outcomes. However, MRD evaluation has thus far relied on flow-cytometry or molecular-based methods, despite the limitations associated with the patchy infiltration of bone marrow (BM) plasma cells and the presence of extra-medullary (EMD). On the contrary, imaging-based sensitive response assessment through the use of functional rather than morphological whole-body (WB) imaging techniques, such as positron emission tomography with computed tomography (PET/CT) and magnetic resonance imaging (MRI), likely is a promising strategy to overcome these limitations in evaluating response to therapy and in the assessment of the MRD status in MM patients. However, despite the significant advances in the development and availability of novel functional imaging techniques for MRD evaluation, a worldwide standardization of imaging criteria for acquisition, interpretation, and reporting is yet to be determined and will be object of future investigations.

Bispecific antibodies (BsAbs) are artificially engineered antibodies that can bind simultaneously to the CD3 subunit within the T-cell receptor complex and an antigen on tumor cells, leading to T-cell activation and tumor cell killing. BsAbs against BCMA or GPRC5D have shown impressive clinical activity in heavily pretreated patients with relapsed/refractory multiple myeloma (RRMM), with some agents having already received regulatory approval after the third (by the European Medicines Agency, EMA) or fourth (by the Food and Drug Administration, FDA) line of therapy; the results of early-phase clinical trials targeting FcRH5 are also promising. Overall, BsAbs as monotherapy correlated with an ORR that exceeded 60%, with a high CR rate ranging between 25% and 50% and a median PFS of around 1 year among patients with a median of 4–6 prior lines of therapy. The main toxicities include cytokine release syndrome, cytopenias, hypogammaglobulinemia, and infections; on-target off-tumor adverse events involving the skin, mucosa, hair, and nails may also occur with anti-GPRC5D BsAbs. Active research to increase their efficacy and improve their tolerance is still in progress, including combination therapies and application in earlier treatment lines and the development of novel agents. A better understanding of the mechanisms of resistance is a challenge and could lead to more personalized approaches.

Modern immunotherapy approaches are revolutionizing the treatment scenario of relapsed/refractory (RR) multiple myeloma (MM) patients, providing an opportunity to reach deep level of responses and extend survival outcomes. Antibody-drug conjugates (ADCs) and T-cell redirecting treatments, including bispecific antibodies (BsAbs) and chimeric antigen receptor (CAR) T cells therapy, have been recently introduced in the treatment of RRMM. Some agents have already received regulatory approval, while newer constructs, novel combinations, and applications in earlier lines of therapy are currently being explored. This review discusses the current landscape and possible development of ADCs, BsAbs and CAR-T cells immunotherapies. ADCs, BsAbs, and CAR-T therapy have demonstrated substantial activity in heavily pretreated, triple-class exposed (TCE) MM patients, and T-cell redirecting treatments represent new standards of care after third (European Medicines Agency, EMA), or fourth (Food and Drug Administration, FDA), line of therapy. All these three immunotherapies carry advantages and disadvantages, with different accessibility and new toxicities that require appropriate management and guidelines. Multiple on-going programs include combinations therapies and applications in earlier lines of treatment, as well as the development of novel agents or construct to enhance potency, reduce toxicity and facilitate administration. Sequencing is a challenge, with few data available and mechanisms of resistance still to be unraveled.

This systematic review examines the available clinical data on CD34+ cell mobilization, collection, and engraftment in multiple myeloma patients treated with the anti-CD38 monoclonal antibodies daratumumab and isatuximab in clinical trials and in real life. Twenty-six clinical reports were published between 2019 and February 2024. Most studies documented lower circulating CD34+ cells after mobilization compared to controls, leading to higher plerixafor requirements. Although collection yields were significantly lower in approximately half of the studies, the collection target was achieved in similar proportions of daratumumab- and isatuximab-treated and nontreated patients, and access to autologous stem cell transplant (ASCT) was comparable. This could be explained by the retained efficacy of plerixafor in anti-CD38 monoclonal antibody-treated patients, while no chemotherapy-based or sparing mobilization protocol proved superior. Half of the studies reported slower hematopoietic reconstitution after ASCT in daratumumab- and isatuximab-treated patients, without an excess of infectious complications. While no direct effect on stem cells was observed in vitro, emerging evidence suggests possible dysregulation of CD34+ cell adhesion after daratumumab treatment. Overall, anti-CD38 monoclonal antibodies appear to interfere with CD34+ cell mobilization, without consistently leading to significant clinical consequences. Further research is needed to elucidate the underlying mechanisms and define optimal mobilization strategies in this patient population.