Cytogenetic Testing by Fluorescence in Situ Hybridization Is Improved by Plasma Cell Sorting in Multiple Myeloma

Accurate detection of cytogenetic abnormalities has become more important for improving risk-adapted treatment strategies in multiple myeloma (MM). However, precise cytogenetic testing by fluorescence in situ hybridization (FISH) is challenged by the dilution effect of bone marrow specimens and poor growth of plasma cells ex vivo . To address these issues, we compared the performances of three different enrichment modalities for FISH: direct FISH, fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms (FICTION) technique, and a plasma cell sorting FISH with fluorescence-activated cell sorter (FACS). We examined cytogenetic abnormalities in bone marrow cells of 493 patients with newly diagnosed MM and compared the efficacy of each modality. FISH disclosed cytogenetic abnormalities in 38.0% of samples by direct FISH, 56.3% by FICTION, and 95.5% by FACS-FISH, and the percentage of cells with abnormal signals detected by FISH was higher by FACS-FISH than direct FISH or FICTION. Our results suggest that the efficacy of FISH is dependent on the plasma cell enrichment modalities and reveal that plasma cell sorting FISH with FACS enables better detection of cytogenetic abnormalities in diagnostic MM samples with low plasma cell frequency.