Solitary plasmacytomas and soft-tissue involvement in multiple myeloma

Abstract

Localized plasmacytomas (solitary plasmacytoma of bone-SPB and extramedullary plasmacytoma-EMP) account for less than 5% of all plasma cell malignancies. The median survival of patients with localized plasmacytomas is longer than 10 years. The rate of progression to multiple myeloma (MM) of SPB and EMP is about 75% and between 10 and 30%, respectively. The current predictors of progression are serum free-light chains, PET imaging, and bone marrow flow cytometry. Treatment consists of radiation therapy. In patients with MM two types of soft-tissue involvement have been recognized: (1) extramedullary (EMD) resulting from hematogenous spread with no contact with bones and (2) paraskeletal consisting of tumor masses arising from bones. The incidence of paraskeletal and EMD involvement at diagnosis ranges from 7 to 34% and from 1.7 to 4.5%, respectively. The incidence of EMD at relapse increases up to 10%. Plasma cells from EMD are more immature showing plasmablastic morphology, CD56 downregulation, and higher frequency of 17p deletion and is more prevalent in patients with GEP-defined high-risk MM. PET/CT is the imaging technique of choice when soft-tissue myeloma involvement is suspected. The prognosis of patients with EMD is worse than those with paraskeletal. Alkylating agents, particularly high-dose melphalan, and bortezomib, are effective for paraskeletal disease with less evidence for EMD. The efficacy of immunomodulatory drugs is limited. In patients non-eligible for autologous stem cell transplantation (ASCT), melphalan, prednisone, and bortezomib (MPV) seem the best treatment option while for those eligible for ASCT a bortezomib-based regimen is the induction of choice. Treatment at relapse should consist of a lymphoma-like regimen followed by SCT whenever possible.