Multicolour spectral karyotyping identifies new translocations and a recurring pathway for chromosome loss in multiple myeloma

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Multicolour spectral karyotyping (SKY) was performed on primary tumour specimens from 100 patients with multiple myeloma (MM) that showed complex clonal chromosome aberrations not fully characterized by G-banding. In this study, SKY was able to identify or revise translocations with breakpoints involving 14q32, 11q13 or 8q24 in 32 patients (32%). Five new recurring translocations were identified, two of which involved chromosome 22. A subtle reciprocal translocation t(14;22) (q32;q11∼12) was identified using SKY in two patients and a second, much larger, translocation t(11;22)(q13;q13) was identified using G-banding in three patients. A third new translocation was identified in two patients using SKY and G-banding as der(7)t(7;7)(p15∼22;q22∼32). Twenty-three patients (23%) showed the loss of 8p by whole-arm translocations with different whole-arm donor chromosomes. Among this group, two new recurring whole-arm translocations involving the centromeric breakpoint 8q10 were identified as der(8;20)(q10;q10) and der(8;18) (q10;q10) in three patients each. In addition, a novel pattern of three-way translocations involving the clonal evolution of the t(8;22)(q24;q11) by the subsequent loss of 8p by whole-arm translocations was found in three patients. The chromosome instability identified here demonstrates that the loss of 8p can occur by multiple whole-arm translocations, indicating a new pathway for the loss of a specific chromosome region in MM.

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