Gene-expression signature of benign monoclonal gammopathy evident in multiple myeloma is linked to good prognosis

Abstract

Monoclonal gammopathy of undetermined significance (MGUS) can progress to multiple myeloma (MM). Although these diseases share many of the same genetic features, it is still unclear whether global gene-expression profiling might identify prior genomic signatures that distinguish them. Through significance analysis of microarrays, 52 genes involved in important pathways related to cancer were differentially expressed in the plasma cells of healthy subjects (normal plasma-cell [NPC]; n=22) and patients with stringently defined MGUS/smoldering MM (n=24) and symptomatic MM (n=351) (P<.001). Unsupervised hierarchical clustering of 351 patients with MM, 44 with MGUS (24+20), and 16 with MM from MGUS created 2 major cluster branches, one containing 82% of the MGUS patients and the other containing 28% of the MM patients, termed MGUS-like MM (MGUS-L MM). Using the same clustering approach on an independent cohort of 214 patients with MM, 27% were found to be MGUS-L. This molecular signature, despite its association with a lower incidence of complete remission (P=.006), was associated with low-risk clinical and molecular features and superior survival (P<.01). The MGUS-L signature was also seen in plasma cells from 15 of 20 patients surviving more than 10 years after autotransplantation. These data provide insight into the molecular mechanisms of plasma-cell dyscrasias.

Figure 1

Expression patterns of 52 genes differentially expressed in PCs of healthy donors (NPC) and patients with MGUS. Two-dimensional unsupervised hierarchical cluster analysis of 52 genes (rows) in CD138-enriched plasma cells from 22 healthy donors and 24 MGUS patients (columns). Mean-centered gene expression is depicted by a normalized-signal pseudocolor scale, as described. Red and green indicate overexpressed and underexpressed genes, respectively. Sample dendrogram (top), reflecting relatedness among samples, consists of 2 major branches defined by overexpressed and underexpressed genes. The left branch consists of 22 NPC samples (horizontal blue bar) and 2 MGUS samples (green arrows), whereas the right branch contains all MGUS (horizontal green bar) and a subset of 2 NPC samples (blue arrows).

Figure 2

Expression patterns of 52 genes segregate MGUS and MGUS-L MM from non–MGUS-L MM. Two-dimensional unsupervised hierarchical cluster analysis of 52 MGUS genes (rows) in CD138-enriched plasma cells of patients with MGUS (n = 56), MM from MGUS (n = 16), and newly diagnosed MM (n = 351) (columns). The left branch consists of MGUS and MGUS-like MM samples (horizontal green bar), and the right branch contains the non–MGUS-L MM (horizontal red bar). Green arrows represent MGUS patients (MM-L MGUS).

Figure 3

Expression levels of the 52 MGUS genes in PC of healthy donors and patients with MGUS and MM. A colorgram of the expression of the 52 genes in NPC (n = 22), MGUS, MM from MGUS (n = 72), and MM (n = 351) (based on their location in either of the 2 major branches of the dendrogram in Figure 2) and multiple myeloma cell lines (MMCLs) (n = 22). MGUS and MM from MGUS on the left side of the figure represent clusters in the MGUS-L MM branch of Figure 2, and those on the right side represent clusters in the non–MGUS-L MM branch. Genes are indicated along the vertical axis and samples on the horizontal axis. The normalized expression value for each gene is indicated by a color, with red representing high expression and blue representing low expression. Note that NPCs have a distinct pattern of overexpressed and underexpressed genes that progressively inverts with transition to MGUS, MGUS-L MM, non–MGUS-L MM, and finally to MMCL.

Figure 4

Box plots of expression profiles of genes exhibiting common patterns. Expression levels of select genes exhibiting progressive loss (top 3 panels), progressive increase (middle 3 panels), or increased followed by decreased expression (bottom 3 panels) across the sample groups, as ordered in Figure 2. Sample groups are plotted along the x-axis, and the natural log-transformed Affymetrix-derived signal is plotted on the y-axis. Top, bottom, and middle lines of each box correspond to the 75th percentile (top quartile), 25th percentile (bottom quartile), and 50th percentile (median), respectively. The whiskers extend from the 10th percentile (bottom decile) and top 90th percentile (top decile). Open circles denote outliers within each group. MGUS and MM from MGUS on the left side of the figure represent clusters in the MGUS-L MM branch of Figure 2, and those on the right side represent clusters in the non–MGUS-L MM branch.

Figure 5

Superior overall survival in MGUS-L MM and non–MGUS-L MM lacking amp1q21. (A) Kaplan-Meier estimates of overall survival in MGUS-L MM and non–MGUS-L MM showed superior 5-year actuarial probabilities of event-free survival (64% vs 44%; P = .001) and overall survival (76% vs 59%; P = .009) in patients with MGUS signature. (B) Kaplan-Meier estimates of overall survival in MGUS-L and non–MGUS-L MM according to presence of amp1q21 by interphase FISH. Amp1q21 was not a significant adverse parameter in MGUS-L MM, but it identified a group at high risk among patients with non–MGUS-L MM.

Figure 6

MGUS-L signature is discernible in a test cohort of patients with newly diagnosed MM enrolled in TT3. As in Figure 2, a 2-dimensional unsupervised hierarchical cluster analysis of 52 genes (rows) in CD138-enriched plasma cells from MGUS (n = 56), MM from MGUS (n = 16), and newly diagnosed MM (n = 214). Green arrows represent MGUS clusters with so-called non–MGUS-L MM.

Figure 7

MGUS-L signature is present in most PCs of patients still alive more than 10 years after TT1. As in Figure 2, a 2-dimensional unsupervised hierarchical cluster analysis of 52 genes (rows) in CD138-enriched plasma cells from patients with MGUS (n = 56), MM from MGUS (n = 16), and newly diagnosed MM (n = 351, training cohort) and from 20 long-term survivors (columns). Long-term survivor samples are indicated by green arrows.