Multiple Copies of MLL Is The Most Commonly Detected Cytogenetic Abnormality In Newly Diagnosed Multiple Myeloma and May Modify Disease Risk

Multiple myeloma (MM) is a heterogeneous condition with variable disease course, response to therapy, and survival outcome. Cytogenetics and fluorescent in-situ hybridization (FISH) have identified several recurrent chromosomal aberrations in MM and play important and independent roles in risk stratification (Munshi et al. Blood 2011). However, the pathogenesis of the disorder remains poorly understood. Next-generation sequencing has recently identified that MM involves mutations of genes with roles in protein translation, histone methylation, and blood coagulation (Chapman et al. Nature 2011). Based on the observation that extra copies of MLL, a histone methyltransferase known to regulate the homeotic transcription factor HOXA9 that is highly expressed in MM, is frequently detected in MM, we sought to define the incidence and prognostic significance of excess MLL in MM patients.

We identified 188 patients with newly diagnosed MM who had cytogenetics and/or FISH performed on initial, pre-treatment bone marrow specimens at Memorial Sloan-Kettering Cancer Center between January 2009 and December 2012. Standard karyotype and FISH were performed as previously described (Cigudosa et al. Blood 1998, Gerritsen et al. Blood 1992). Probes included LSI IgH/FGF3, LSI IgH/CCND1, LSI IgH/MAF, LSI MLL, LSI p53/cep17, LSI13q14.3/13q34, LSI ETV6, LSI CBFB, LSI 1p36/1q25, and LSI 5,9,15 from Abbott Molecular. Fisher's exact test evaluated the association between MLL and selected abnormalities. Kaplan-Meier methodology estimated overall survival from the date of BM evaluation, and survival was compared using a logrank test.

In unselected bone marrow specimens, abnormalities were detected by karyotype in 17% (27/156) and FISH in 47% (87/186) of patients tested. Hyperdiploidy, which has been associated with longer survival, was identified in 23% (43/187) of patients, while the unfavorable risk abnormalities, including loss of p53, deletion 13q (by karyotype), translocation (4;14) and excess 1q were seen in 8% (15/179), 8% (12/156), 4% (7/176) and 16% (29/178) of patients, respectively. Translocation (11;14) was seen in 4 patients; translocation (14;16) was not identified in any patient. 28% (51/183) of patients had extra copies of MLL, which was the most frequent genetic abnormality identified. Unexpectedly, this abnormality was significantly associated with both favorable (hyperdiploidy, P = <0.001) and unfavorable (deletion 13q, P = 0.043; excess 1q P = 0.001) risk genetics. While having excess MLL had no impact on the overall survival of standard-risk patients, defined as neither hyperdiploid nor with unfavorable genetics (N = 100), patients with poor-risk genetics (N = 46) and extra copies of MLL had a trend toward better survival, P = 0.06 (Figure 1).

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Karyotype and FISH studies identified excess MLL as the most frequent cytogenetic abnormality in a large cohort of newly diagnosed MM patients. In patients with MM and unfavorable cytogenetics, the presence of excess MLL may ameliorate some of the adverse impact of associated with these abnormalities. Understanding the functional significance of excess MLL, perhaps as it relates to frequently dysregulated HOXA9 in MM, may provide insight into disease pathogenesis and/or identify drugable targets.

No relevant conflicts of interest to declare.