Abstract
Multiple myeloma is biologically and clinically a complex and heterogeneous disease which develops late in life, with the median age at the time of initial diagnosis being 66 years. In 1975, Durie and Salmon developed the first broadly adopted staging system in multiple myeloma, and in the ensuing decades, the risk stratification tools have improved and now incorporate different parameters to better predict the prognosis and to guide the treatment decisions. The International Staging System (ISS) was initially developed in 2005, revised in 2015 (R-ISS), and again in 2022 (R2-ISS). Tremendous progress has been achieved in multiple myeloma therapy over the past 25 years with the approval of immunomodulatory drugs, proteasome inhibitors, and anti-CD38 monoclonal antibodies, resulting in a major paradigm shift. The dysfunction of the innate and adaptive immune system, especially in the T cell repertoire, represents a hallmark of multiple myeloma evolution over time, supporting the need for additional therapeutic approaches to activate the host's immune system and to overcome the immunosuppressive tumor microenvironment. Novel T cell-directed therapies include chimeric antigen receptor (CAR) T cell therapies and bispecific antibodies that leverage the immune system's T cells to recognize and attack the tumor cells. Second-generation anti-BCMA CAR T cell therapies and bispecific antibodies that bind the tumor antigen BCMA or GPRC5D onto myeloma cells and CD3 on the T cell's surface are currently available for the treatment of relapsed/refractory multiple myeloma. Despite impressive results obtained with currently approved treatments, multiple myeloma remains incurable, and almost all patients eventually relapse. Moreover, patients with extramedullary disease and plasma cell leukemia represent an unmet medical need that require additional strategies to improve the outcome. In this review, we provide an overview of the evolution of risk stratification and the treatment of multiple myeloma.