Multiple Myeloma Precursor Disease

Diagnosis showed monoclonal gammopathy of undetermined significance (MGUS), and an M protein level that remained relatively stable for approximately 10 years before rapidly increasing in 2009.
^aBone marrow biopsy performed in November 2009.
^bBone pain reported in January 2010.

The diagnosis of smoldering myeloma was determined from a bone marrow biopsy. A, Hematoxylin-eosin staining shows 30% to 50% marrow cellularity. B, Immunostaining for CD138 (brown chromagen; hematoxylin counterstain) shows 40% CD138+ cells. Based on the 2010 International Myeloma Working Group criteria,¹ CD138 staining of the marrow core is the reference standard for determining percentage of plasma cells. C and D, Immunostaining for free κ light chains (C) and free λ light chains (D) using a brown chromagen and hematoxylin counterstain shows a κ light chain restriction pattern with almost no λ-positive plasma cells. Immunohistochemistry for CD138 (B-A38; Cell Marque) and κ and λ light chains (DAKO, Carpinteria, California) was performed on Ventana using an Ultra View DAB detection kit (Ventana Medical Systems, Tucson, Arizona). CD138 staining of the marrow core was used as the criterion standard for determining percentage of plasma cells (original magnification × 100 for all photomicrographs).

A, Plasma cells were gated for analysis (indicated by blue border) based upon characteristically bright (increased) CD38 expression; plasma cell differentiation was further confirmed by the expression of CD138 in this population (C). By flow cytometry, 12% of cells were plasma cells compared with 40% plasma cells by immunohistochemistry. This much lower percentage of plasma cells was due to hemodilution, precluding the use of flow cytometry to quantitatively analyze the percentage of plasma cells. B and C, Antigen-negative populations are located in the 1-to-10 region of the scales. B, Analysis for κ and λ light chains demonstrated κ light-chain restriction. C, Almost all plasma cells were found to be immunophenotypically abnormal: CD38-positive, CD45-negative, CD19-negative, and dim (decreased) CD27 expression.

Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) showed metabolically active and anatomically visible lesions (arrowheads) in the sacrum (standard uptake value [SUV] 3.4) and the iliac bone (SUV 2.8).

The biological transition from normal plasma cells to multiple myeloma precursor disease (monoclonal gammopathy of undetermined significance [MGUS] and smoldering myeloma) to multiple myeloma consists of many overlapping oncogenic events. These events do not all occur in each affected individual, eg, hyperdiploidy is present in approximately 50% of precursor and multiple myeloma tumors. In this illustration, solid lines approximate the period during which the oncogenic event is likely to occur; dashed lines indicate less certainty in the timing. Once an oncogenic event occurs, it almost always persists. The 2 major types of early events include IgH translocations [most commonly: t(4;14), t(14;16), t(6;14), t(11;14), and t(14;20)] and hyperdiploidy, although most tumor cells have only 1 of these 2 events. Either of these can coexist with deletion of chromosome 13, although this abnormality most commonly (>80% to 90% of patients) occurs with the t(4;14), t(14;16), and t(14;20) IgH translocations.^15- 16 A unifying early event in most, perhaps all, precursor and multiple myeloma tumors is the dysregulation of a cyclin D gene. Secondary translocations, sometimes involving an Ig locus, can occur at any stage of myelomagenesis. Activating mutations of NRAS and KRAS are each present in about 15% of multiple myeloma tumors; NRAS mutations are present in MGUS tumors while KRAS mutations are absent from MGUS tumors. Constitutive activation of the nuclear factor κB (NFκB) pathway is mediated by mutations in some tumors during progression.¹⁷ Other events, such as Rb gene inactivation or deletion of p53 or p18 genes, are mostly seen at the level of advanced intramedullary or extramedullary multiple myeloma.^15,18 Through the stage of intramedullary multiple myeloma the tumor cells are strongly dependent on the bone marrow microenvironment.¹⁹ The reciprocal interaction of the bone marrow microenvironment and the tumor cells results in changes in the bone marrow microenvironment, which are responsible for the lytic lesions that are characteristic of multiple myeloma. Extramedullary tumor cells have developed features that make them independent of the bone marrow microenvironment.