CKS1B Over-Expression Significantly Predicts for a Lower Rate of Response to Primary Therapy with Thalidomide-Dexamethasone (Thali-Dex) for Newly Diagnosed Multiple Myeloma (MM) Patients.

In MM tandem duplication and jumping translocations of the q21 band of chromosome (chr.) 1 are acquired during progression of the disease and can lead to chr.1q amplification. In several studies, chr. 1 amplification has been linked to poor prognosis after both conventional and high-dose chemotherapy. Recently, a subset of genes mapping on 1q21 band has been identified, whose increased expression may be due to increased DNA copy number. Among these genes, CKS1B has been one of the most significantly upregulated. CKS1B regulates SCF skp2 mediated ubiquitination and proteolysis of the cyclin dependent kinase inhibitor p27^Kip1, whose low expression has been reported to be an independent adverse prognostic factor in MM patients. Aim of the present study was to investigate the relationship between CKS1B expression and response to primary therapy with thali-dex in a large series of patients with newly diagnosed MM. Secondary endpoint was to explore the relationship between CKS1B expression and del(13), as assessed by FISH analysis, and t(4;14), as evaluated by an RT-PCR assay designed to detect the presence of IgH/MMSET fusion gene. A total of 132 patients were analyzed. The presence of t(4;14) and CKS1B expression were investigated in all patients, while del(13) was studied in 129/132 patients. CKS1B expression was evaluated by Real-time RT-PCR. CKS1B values were separated in four different quartiles, with expression levels increasing progressively from quartile 1 to 4. Response to therapy was evaluated according to the criteria proposed by Bladè et al. The Fisher test and the Mann-Whitney test were applied for statistical analysis. On an intent-to-treat basis, the overall probability to respond (≥ partial response, PR) to up-front thali-dex therapy was 71%, while 38 patients (29%) either did not respond (NR) or progressed. Median CKS1B expression value was significantly higher in NR in comparison with patients who attained at least a PR: 1.42 (range 0.15–52.35) vs. 0.89 (range 0–11.88), respectively (p=0.01). In particular, the proportion of NR patients in the CKS1B expression quartile 4 was significantly higher as opposed to the frequency of NR in the CKS1B expression quartiles 1 to 3 (45.5% vs. 23.2%, respectively; p= 0.02). CKS1B over expression did not correlate with the presence of t(4;14) or del(13). Only 6 patients harbouring t(4;14) fell into the CKS1B expression quartile 4, as opposed to 32 patients included into the CKS1B expression quartiles 1–3 (18.2% vs. 32.3%; p, not significant). Similarly, the frequency of del(13) was comparable in the CKS1B expression quartile 4 and in the CKS1B expression quartiles 1–3 (34.4% vs. 44.3%; p, not significant). Likewise, only 2 patients carrying both t(4;14) and del(13) fell into the CKS1B expression quartile 4, as opposed to 15 patients who fell into the CKS1B expression quartiles 1–3 (6.5% vs. 15.3%; p, not significant). In conclusion, in patients with newly diagnosed MM, CKS1B over expression at baseline predicts for a significantly lower probability of response to primary remission induction therapy with thali-dex. Poor response to thali-dex conferred by CKS1B over expression is independent from the presence of t(4;14) and/or del(13). Supported by Università di Bologna, Progetti di Ricerca ex-60% (M.C.); Ministero dell’Università e Ricerca Scientifica (MIUR), progetto FIRB, RBAU012E9A_001 (M.C.); and Fondazione Carisbo.