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

Multicolour spectral karyotyping (SKY) was performed on primary tumour spec imens from 100 patients with multiple myeloma (MM) that showed complex clon al chromosome aberrations not fully characterized by G-banding. In this stu dy, SKY was able to identify or revise translocations with breakpoints invo lving 14q32, 11q13 or 8q24 in 32 patients (32%). Five new recurring translo cations were identified, two of which involved chromosome 22. A subtle reci procal translocation t(14;22) (q32;q11 similar to 12) was identified using SKY in two patients and a second, much larger, translocation t(11;22)(q13;q 13) was identified using G-banding in three patients. A third new transloca tion was identified in two patients using SKY and G-banding as der(7)t(7;7) (p15 similar to 22;q22 similar to 32). Twenty-three patients (23%) showed t he loss of 8p by whole-arm translocations with different whole-arm donor ch romosomes. Among this group, two new recurring whole-arm translocations inv olving 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 patt ern of three-way translocations involving the clonal evolution of the t(8;2 2)(q24;q11) by the subsequent loss of 8p by whole-arm translocations was fo und in three patients. The chromosome instability identified here demonstra tes that the loss of 8p can occur by multiple whole-arm translocations, ind icating a new pathway for the loss of a specific chromosome region in MM.