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Bortezomib is an active agent for treatment of multiple myeloma (MM) and may even be effective in patients (pts) with adverse prognostic factors including unfavorable cytogenetic abnormalities. However, it is unknown whether or not bortezomib may overcome the negative prognostic impact of a CKS1B gene amplification at chromosome 1q21 (amp1q21), which has recently been reported as a negative prognostic factor even in the setting of a total therapy approach. We therefore evaluated chromosome 1q21 among other abnormalities in 46 pts with relapsed/refractory MM who were treated with single-agent bortezomib (1.3 mg/m2 on days 1, 4, 8, and 11 every 3 weeks). Median age of pts was 63 years (range, 40 – 82 ) and median time to bortezomib therapy was 40 months (median number of prior therapies: 3; 96% of pts had high-dose pulsed dexamethasone, 61% thalidomide, 85% alkylating agents, and 41% high-dose melphalan). A response to bortezomib was noted in 45% of pts, with 17% of pts achieving a CR/near CR. Amp1q21 as determined by interphase FISH was observed in 20 of the 46 pts (43.5%). Treatment outcome after bortezomib was negatively affected by presence of amp1q21: The overall response rate was 30% (versus 58% in pts with normal 1q21; P = .06) and the CR/near-CR rate was 10% (versus 23%). Moreover, amp1q21 was associated with shortened time to treatment failure (median, 2.4 versus 6.6 months; P = .043) and overall survival (OS) (median, 4.4 versus 19.8 months; P = .003) compared to pts with normal 1q21. Beta-2-microglobulin and 14q32 translocations were unrelated to treatment outcome with bortezomib. In contrast, median OS was short in the presence of low serum albumin (4.8 versus 17.8 months; P = .036) and deletion of 13q14 (6.7 months versus median not yet reached; P = .06). Using amp1q21, low serum albumin, and deletion of 13q14 as risk factors, patients with significantly different median OS after bortezomib treatment were discriminated: Pts with ≥ 2 risk factors had a median OS of only 4.9 months as opposed to pts with 1 risk factor (median OS 16.5 months) or without any risk factor (median OS not yet reached) (P = .004). In conclusion, FISH-defined amp1q21 is a strong adverse prognostic factor for pts with relapsed/refractory MM treated with single-agent bortezomib. We are currently investigating whether or not bortezomib combinations may be more effective in MM pts with amp1q21.