Detection of chromosome 13q deletions and IgH translocations in patients with multiple myeloma by FISH: comparison with karyotype analysis

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by frequent 13q deletions and IgH translocations that have clinical prognostic significance. We evaluated clonal plasma cells by interphase fluorescence in situ hybridization (FISH) and combined with immunofluorescence detection of cytoplasmic light chain (cIg-FISH) for the presence of 13q deletions and IgH translocations. The FISH results were compared with conventional cytogenetic analysis. Of the 25 bone marrow specimens from MM patients, 11 (44%) had 13q deletions. IgH translocations involving cyclin D1 (t(11;14)) and FGFR3 (t(4;14)) were found in 32 and 36%, respectively. P53 deletions were detected in 20% of the cases. One patient had coexistence of t(11;14) and t(4;14), which has not been previously reported. Conventional cytogenetic analysis was performed in 15 cases and revealed complex numerical and structural changes in 7. Karyotype analysis failed to detect 3 of 6 cases with 13q deletions, and also missed most of the IgH translocations and p53 deletions detected by cIg-FISH. On the other hand, the complex numerical and structural changes shown by conventional cytogenetics were not demonstrated by interphase FISH. Since 13q deletions, IgH translocations and a hypodiploid karyotype are significant prognostic factors for MM, our study illustrates the importance of combining conventional cytogenetics with interphase FISH analysis in patients with MM.