Interphase fluorescence in situ hybridization in multiple myeloma and monoclonal gammopathy of undetermined significance without and with positive plasma cell identification: analysis of 192 cases from the Region of Southern Denmark

Interphase fluorescence in-situ hybridization (i-FISH) was used to investigate 192 patients with multiple myeloma (MM; n = 182) and benign monoclonal gammopathy of undetermined significance (MGUS; n = 10). Of the 182 MM cases, 132 were investigated without and 50 with positive plasma cell identification (PC-ID+); 134 were investigated at diagnosis, 32 at time of progression, 7 at time of relapse, and 9 were investigated with partial remission or no response. The FISH analysis detected 11q23 (n = 61), 13q13∼q14 (n = 181), 14q32 (n = 121), 17p13.1 (n = 181), t(4;14) (n = 76), and t(11;14) (n = 73). Of the 132 patients investigated without PC-ID+, 61 (46%) showed chromosomal abnormalities, compared with 45 of 49 of evaluable cases (92%) with PC-ID+. The increase in abnormal cases identified was due mainly to the detection of more cases with 13q−, 17p−, and der(14)(q32). G-banding cytogenetics was performed in 72 patients; abnormalities were revealed in 19 cases (26%). Concordance between G-banding and i-FISH for one or more aberrations was found in 14 patients. Translocation (11;14) was detected by both methods in four of five cases. In four out of seven cases with either near-tetraploidy/triploidy or hypoploidy in the G-banded karyotypes, the modal number in the G-banded karyotypes could not be elucidated with certainty with i-FISH. Three of the 10 MGUS patients showed abnormalities. In conclusion, PC-ID+ is important for the detection of structural aberrations and disclosing translocations involving 14q32. Of these, translocations t(4;14) constituted 9% and t(11;14), 20%. Finally, based on the small number of cytogenetically abnormal cases, it is recommended to include cytogenetics (and, for example, the DNA index) in the prognostic armamentarium.