Oral and Poster Abstracts
651. Myeloma: Biology and Pathophysiology, excluding Therapy: Poster II
Sunday, December 8, 2013, 6:30 PM-8:30 PM, Hall G (Ernest N. Morial Convention Center)
Introduction: Monoclonal gammopathy of undetermined significance (MGUS) progresses to asymptomatic (AMM) or symptomatic myeloma (MM) at an annual rate of 1%. Primary cytogenetic aberrations of chromosome 14q32 translocations with one of the partner genes (MMSET, FGFR3, CCND3, CCND1, MAF, and MAFB), and secondary mutations, such as gain of 1q21 and deletion of 17p13 (TP53 locus), have been detected at diagnosis and during disease progression of MGUS or AMM (Lopez-Corral et al, Clin Cancer Res 2011). The goals of this study were to understand the underlying genetic features of MGUS and AMM, and define significant biomarkers for MGUS and AMM in disease progression.
Methods: Bone marrow aspirates were obtained from 221 patients with MGUS or AMM. Of 118 patients initially diagnosed with MGUS, 13 (11%) progressed to AMM or MM, while 29 of 103 (28%) patients initially diagnosed with AMM progressed to MM. In an attempt to characterize the immunoglobulin heavy chain (IGH) gene in MGUS and AMM, bone marrow clonal plasma cells (PCs) were analyzed using interphase fluorescence in situ hybridization (FISH) with two probes at 14q32 for the IGH regions. Specially, the IGH constant region (IGHC) and variable region (IGHV) were simultaneously probed to investigate the overall patterns of rearrangement. The IGHC probe is comprised of 240kb DNA sequences from IgG4 to IgM. The IGHV probe is comprised of 150kb DNA sequences from IgV3-20 to IgV7-34. Clonal PCs in the bone marrow aspirates were identified using kappa (κ) and lambda (λ) light chain restrictions. 14q32 translocations were determined based on gene expression levels of each of the partner genes combined with FISH of fusions of either the IGHC or the IGHV probe and a probe of the partner gene. Gain of 1q21 and deletion of TP53 locus were routinely performed on newly diagnosed patients.
Results: We found highly-diversified IGHC and IGHV signal patterns (Table) in MGUS in comparison to the predominance of a single FISH pattern in AMM/MM. In MGUS, the heterogeneous IGHC/V patterns were observed in both the κ and λ light chain restricted populations; however, none of the PC clones comprised a dominant population (>50%), also reflected in low-risk serum free light chain (sFLC) ratios (<100). As MGUS progressed to AMM or MM, a PC clone with a homogeneous IGHC/V pattern emerged in either the κ or λ light chain restricted PC population. In AMM, 10% of the patients with a FISH-detected dominant PC clone and a significant high-risk sFLC ratio (≥100) progressed to MM within the first 2 years; 18% of the patients whose sFLC ratios did not meet disease progression criteria, yet had a dominant PC clone in the bone marrow by FISH, also progressed to MM. This may be attributed to PCs with a non-secretory phenotype. Interestingly, the frequency of all 14q32 translocations in these patients (42%) was similar to that of 14q32 translocations in patients with MM, especially t(11;14), which was present in 20% of the cases. However, while t(4;14) was less frequent in MGUS/AMM than in MM, the patients had twice the frequency of t(14;16) than in patients with MM. Among t(4;14) in MGUS and AMM, IGH/MMSET translocations were observed at both stages, but, IGH/FGFR3 translocations were only present in AMM. The cytogenetic feature of 1q21 gain and TP53 deletion were primarily detected in AMM. In conclusion, IGHC and IGHV probes for FISH may serve as clinically relevant biomarkers to identify MGUS and AMM on the basis of plasma cell clonality. The chromosomal translocations and secondary cytogenetic mutations may indicate disease progression even at the antecedent stages. IGHC/V FISH patterns are a promising tool that may be especially valuable in bone marrow specimens with a background of polyclonal plasmacytosis to characterize patients presenting with MGUS or AMM for improved diagnosis, prognosis, and treatment.