26 Additional diagnostic yield identified through the application of expanded genomic testing: validation of an RNA sequencing panel for multiple myeloma

Tara J Spence^1,2*

Emily Fullerton²

Christina Turpin²

Bob Argiropoulos^1,2

¹Constitutional Cytogenetics Laboratory, Genetics and Genomics South, Alberta Children’s Hospital, Calgary, AB, Canada

²Cancer Cytogenetics Laboratory, Genetics and Genomics South, Diagnostic and Scientific Centre, Calgary, AB, Canada

Objectives

Multiple myeloma (MM) is characterized by proliferation of clonal plasma cells in the bone marrow. In the Cancer Cytogenetics Laboratory, we currently use fluorescence in situ hybridization (FISH) to assess for the presence of specific chromosomal translocations involving the IGH locus on chromosome 14, including the t(4;14)(IGH;FGFR3), t(11;14)(CCND1;IGH) and t(14;16)(IGH;MAF) fusions. These diagnostic and prognostic events guide treatment decisions. However, there are additional genetic alterations that are not routinely tested in current practice.

Methods

Validation was performed on 99 MM samples on the Illumina TruSight RNA Fusion Panel that were previously evaluated using the MM FISH panel for t(4;14), t(11;14) and t(14;16) for translocations involving the IGH locus, resulting in elevated expression of FGFR3, CCND1, and MAF, respectively. Expression profiles were compared to prior diagnostic FISH analysis.

Results

All samples (36 of 36) reported as positive by FISH were concordantly positive by RNA expression analysis with no false negatives identified. Furthermore, 42% (42 of 99 samples) of our validation cohort had additional clinically relevant findings that would not have been detected by standard FISH testing. These included overexpression of CCDN2 (n=4), CCND3 (n=8), MAFA (n=1), MAFB (n=3) due to rarer translocation events, detection of CCND1 overexpression (n=4) in samples previously reported negative by FISH, identification of MYC overexpression (n=18), and an elevated BCL2/BCL2L1 ratio (n=13) which has therapeutic implications.

Conclusions

Implementation of RNA expression analysis results in significant additional findings with important implications in prognostication and novel therapeutics for MM. With the replacement of standard FISH testing, there is enormous opportunity for expanded clinical and diagnostic …