Date Published: June 12, 2012
Publisher: Wiley Subscription Services, Inc., A Wiley Company
Author(s): Carina S Debes Marun, Andrew R Belch, Linda M Pilarski.
Chromosomal abnormalities in plasma cells (PCs) from multiple myeloma (MM) provide a clonal signature to identify malignant cells. BM-lymphocytes from MM aspirates, defined by stringent criteria, were screened for the same chromosomal abnormalities as autologous PCs, including translocations, deletions, and amplifications. For 200 MM patients, we evaluated BM mononuclear cells to identify lymphocytes and autologous PCs on the same slide, followed by interphase fluorescence in situ hybridization to characterize their chromosomal abnormalities. Of all patients having a given chromosomal abnormality(s) in PCs, 45% showed that same abnormality(s) in 2–37% (median = 5%) of BM-lymphocytes. Most translocations, amplifications, and deletions found in MM PCs were also detected in lymphocytes, above the healthy-donor “cut-off.” In patients having chromosomally abnormal CD20− PCs, chromosomally abnormal lymphocytes were found among CD20+ cells confirming them as B cells. Exceptions were amplification of 1q21 or p53 deletion, which characterize PCs but were undetectable in BM-lymphocytes, suggesting that processes leading to these abnormalities may be exclusive to PCs. For a set of 75 patients whose BM-lymphocytes and PCs were analyzed by all six probe sets, 58% of those with abnormal PC also had abnormal BM-lymphocytes harboring from one to five different abnormalities. Confirming the clinical significance of chromosomally abnormal BM-lymphocytes, MM patients having abnormalities in both lymphocytes and PC had significantly worse survival than those with abnormalities only in PC (HR = 2.68). The presence of at least one chromosomal abnormality in BM-lymphocytes appears to have greater clinical significance than particular abnormalities. Chromosomally abnormal BM-lymphocytes correlate with poor outcome and by extrapolation with more aggressive disease.
Multiple genetic abnormalities have been described in multiple myeloma (MM), including numerical abnormalities and structural changes such as translocations, duplications, inversions, and amplifications. The most common numerical change is monosomy of chromosome 13 [1–5] with infrequent interstitial deletions [6, 7] and trisomies of chromosomes 3, 5, 9, 11, 15, and 21 [5,8]. The most common structural abnormalities are translocations of IgH locus and amplification of 1q21 . The IgH translocation partner remains unidentified in roughly 50% of MM cases having a 14q32 translocation. Several recurrent IgH translocation partners have been identified, including 11q13 (15–20%), 4p16 (5–15%), 16q23 (2–5%), 6p21 (5%), and 20q12 (2%) [10–16]. Some chromosomal abnormalities appear early in malignant development, such as the primary IgH translocations or deletion of chromosome 13, and others appear to be late acquisitions as the MM clone evolves, such as p53 deletion or 1q21 amplification [1, 17]. Although no unique abnormality characterizes all MM, those harbored by the plasma cell (PC) in each patient represent clonotypic markers to identify clonal relationships within that MM patient.
Using stringent morphologic criteria to define lymphocytes and PC, we show here that for all analyzed MM patients having at least one chromosomal abnormality in their PCs, 45% also have at least one such abnormality in their BM-lymphocytes, shown for a subset of patients to include CD20+ cells. This approach avoids any need to make assumptions about the phenotypes comprising the MM clone, given that purification of B-cells potentially excludes important sets of CSC. We screened BM-lymphocytes for IgH translocations, deletions/amplifications, and numerical abnormalities and identified a total of 17 different numerical or structural abnormalities in PC, nearly all of which were also detected in BM-lymphocytes of at least some patients. Furthermore, analysis of OS revealed that patients who had at least one chromosomal abnormality in both BM-lymphocytes and PC had significantly worse survival than did those patients having abnormalities only in their PCs. When all 200 patients were included in the analysis, regardless of the chromosomal status of their PCs, patients with at least one abnormality in their BM-lymphocytes still showed significantly worse survival independent of treatment type(s). Based on individual chromosomal abnormalities, only del13, translocation t(4;14), and trisomy1 showed a correlation with OS. The presence of chromosomal abnormalities in BM-lymphocytes provides strong evidence for their participation in the malignant process in MM, perhaps as CSC, as well as a marker for their identification. The presence or absence of any particular chromosomal abnormality may be of less clinical significance than the fact that abnormal lymphocytes populate the BM, and their presence correlates with reduced survival.