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KEY CONCEPTS

  • The updated International Myeloma Working Group (IMWG) criteria for multiple myeloma includes patients with bone marrow plasmacytosis of at least 60%, an involved-to-uninvolved serum-free light-chain ratio of at least 100, or more than one focal lesion on magnetic resonance imaging (MRI) studies of at least 5 mm in size in addition to the criteria of hypercalcemia, renal disease, anemia, and bone disease (CRAB).

  • The IMWG now recommends advanced imaging, such as whole-body low-dose computed tomography (CT), positron emission tomography–computed tomography (PET-CT), or MRI to evaluate for bone disease because it can detect up to 80% more lesions compared with plain film radiographs.

  • Triplet therapies, such as with a proteasome inhibitor, immunomodulatory drugs, and steroids have shown significant improvement over doublet therapy. Ongoing trials are investigating quadruplet therapy, with promising initial results, and they could become standard of care in the future.

  • As of 2020, autologous transplant after induction chemotherapy remains the standard of care and has shown significant improvement in progression-free survival. This might change in the future depending on disease risk status, and minimal residual disease testing.

  • Maintenance therapy after autologous transplant is recommended because it has been shown to significantly improve progression-free survival.

  • As of 2020, there is no indication to treat patients with smoldering myeloma. However, this could change in the future, because recent trials have shown that treatment of high-risk smoldering myeloma can potentially delay its progression to myeloma.

INTRODUCTION

Plasma cell dyscrasias are heterogeneous disorders arising from the proliferation of a monoclonal population of plasma cells. Some of these disorders can present serendipitously as benign processes that can be observed; others are highly aggressive and require immediate intervention. The most common plasma cell dyscrasia is monoclonal gammopathy of undetermined significance (MGUS), a benign condition that can be observed. Related disorders include smoldering multiple myeloma (SMM), multiple myeloma (MM), solitary plasmacytoma of the bone, extramedullary plasmacytoma, Waldenström macroglobulinemia, primary amyloid light-chain amyloidosis, heavy-chain disease, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome, and TEMPI (telangiectasias, elevated erythropoietin and erythrocytosis, monoclonal gammopathy, perinephric fluid collection, and intrapulmonary shunting) syndrome. The spectrum of MGUS, SMM, and MM represents a natural progression of the same disease. This chapter focuses on the etiology, genetics, biology, diagnosis, clinical features, and current therapy of MM.

Major recent discoveries have changed the way we understand, diagnose, and treat plasma cell dyscrasias. The initial sequencing of the myeloma genome and single-cell genetic analysis paved the way for the concept of intraclonal heterogeneity and Darwinian selection of clones. Increasingly sensitive diagnostic and monitoring techniques allow for more accurate diagnosis, minimal residual disease (MRD) monitoring, and detection of early relapse. New diagnostic criteria for MM have been implemented, and the introduction of novel classes of agents such as immunomodulatory drugs and proteasome inhibitors has led to improved overall survival. In addition, immunotherapy using monoclonal antibodies against different myeloma targets including CD38 and SLAMF7 (CS1) has significantly improved outcomes ...

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