Cytoplasmic Immunoglobulin Fluorescence In Situ Hybridization (cIg FISH) Enhances the Quantitative Detection of Chromosome Abnormalities In Plasma Cell Neoplasms Compared to Conventional FISH

Abstract 1198 Risk stratification of plasma cell neoplasms (PCNs) has become an integral part of clinical management along with the rapid advances in treatment. Cytogenetics is widely performed at diagnosis but has a low abnormality detection rate due to poor proliferation of plasma cells (PCs) in culture and inability to identify cryptic translocations. Conventional interphase FISH improves detection sensitivity, but lacks specificity since the percentage of PCs is diluted by the large number of normal bone marrow cells due to the indiscriminative analysis of all cells by FISH. The International Myeloma Working Group recommends all FISH tests for myeloma be PC specific by either PC enrichment or identifying PCs by cytoplasmic immunoglobulin staining (cIg FISH). However, the real benefits of cIg FISH compared to conventional FISH have never been demonstrated in a controlled study. In this objective comparative study, 75 paired samples from patients with PCNs were analyzed concurrently by conventional FISH and cIg FISH with probes for t(4;14), t(11;14), t(14;16), -13/13q (RB1/LAMP1), 17p- (TP53) and CEP3. For conventional FISH, a minimum of 200 nuclei were scored per probe set. For cIg FISH, 100 cIg positive cells were scored per probe with a minimum of 25 cIg+ cells required for conclusive reporting. In this study, 51/75 cases met the above criteria for direct comparison (see Table). cIg FISH results demonstrated an improved overall detection rate [-13/13q: 53% vs. 45%; 17p - : 14% vs. 12%; t(11;14): 25% vs. 24% and t(4;14): 14% vs.12%]. Impressively, cIg FISH quantitatively identified a much higher proportion of abnormal PCs in all cases. The median % of abnormal PCs with all probes was >50% by cIg FISH but no more than 10% by conventional FISH. The abnormal PCs detected by cIg FISH were >90% of cIg+ cells in 18 cases with at least one probe. In contrast, the abnormal PCs detected by conventional FISH were Disclosures: Jagannath: Celgene: Honoraria; Millenium/Takeda Pharma: Honoraria; JJ Onyx: Honoraria; Merck: Honoraria.