58. Myeloma FISH - Lessons learned from a panel redesign

Abstract

FISH testing on plasma cell (PC)-enriched bone marrow aspirates is routinely used in the genetic workup of patients with PC neoplasms/multiple myeloma (PCN/MM). Despite enrichment, these samples may exhibit low cellularity, requiring panel design that maximizes assessment of core and emerging markers at highest diagnostic yields. We performed a retrospective analysis and validation work accompanying updates to our MM FISH panel (MMP) which consisted of six hybridizations: IGH::CCND1, IGH::FGFR3, IGH::MAF, IGH::MAFB, 1q CKS1B/17p TP53, and +9 JAK2. The update incorporated previously validated 1p CDKN2C/1q to routinely assess for high risk 1p deletions with 1q gain/amp, and a new 17p/17q probe set. Internal analysis of near 1600 total MMPs with 400 positive +9 (3 or 4 copies) cases showed removal of JAK2 to retain six total hybridizations could result in 5% or 2.5% reduced diagnostic yield amongst abnormal or all cases, respectively, though this loss would be offset by CDKN2C (seen in approximately 10% of MM cases). Amongst positive +9 cases, alternative prognostically significant findings (IGH, 1q, 17p) were seen in 44% and cooccurring +11 ploidy assessment in 40%. Validation of 1p/1q and TP53 probes assessed multiple vendors and hybridization configurations to optimize diagnostic yield, quality, and workflows. Known negative samples are used to establish reference ranges and known negative/positive samples by orthogonal FISH and/or genomic microarray are used for accuracy and precision. An unexpected false negative deletion case was encountered during TP53 accuracy, highlighting consideration for expected and potential patterns of the targeted aberration that may occur during clinical testing.