Elevated Expression of CKS1B at 1q21 Is Highly Correlated with Short Survival in Myeloma.

The variability in survival among patients with myeloma can range from months to >10 years. Patients at highest risk are best identified by the presence or absence of an abnormal karyotype found by conventional cytogenetics. However, this test only accounts for ~15% of the variability in outcome. Thus, many patients who present with no cytogenetic abnormalities experience rapid relapse and early death. To better define high-risk disease and also potentially identify specific genetic mechanisms that give rise to this poor survival, we analyzed the gene expression patterns in freshly isolated plasma cells from 40 newly diagnosed myeloma patients who were then treated with high-dose therapy and tandem stem cell transplants. Patients were separated into two groups of 20. Those in the “short-survival” group all died within 900 days of therapy initiation due to disease progression. Patients in the “long-survival” group had all survived >1453 days since therapy initiation. RNA from plasma cells was labeled and hybridized to the U133Plus2.0 microarray containing ~33,000 genes. The expression value was transformed by the log base 2 and each sample was normalized to give a mean of 0 and a variance of 1. Chi-square analyses and t-tests were performed to identify genes whose expression patterns were unique to each group. Kaplan-Meier analysis of overall survival using expression level quartiles was used to demonstrate links to outcome. A total of 1770 probe sets were significantly differentially expressed between the two groups (P <.05). A total of 1025 (58%) of the probe sets were up-regulated in the short-survival group. The chromosomal map positions of all 1770 probe sets were determined; 19% mapped to chromosome 1. Of the 1770 probe sets, 84 demonstrating a >2-fold difference in expression were further analyzed with Kaplan-Meier survival analyses. In this test, 18 probe sets representing 17 genes were highly significant (P <.0001). Of the 17 genes identified, 10 map to chromosome 1; all 4 genes from the p arm were down-regulated while all 6 genes from the q arm were up-regulated in the short-survival group. We have previously demonstrated that jumping 1q and amplification of genes from 1q21 represent common genetic lesions in myeloma. We then examined by FISH, BCL2 and IL-6R showed highly variable over-expression in patient subsets, unrelated to outcome. CKS1B, an evolutionarily conserved protein that interacts genetically and physically with cyclin-dependent kinases and promotes mitosis, is located very near the 1q21 amplification and is over-expressed in myelomas with a short survival. Using FISH analysis with probes specific for these genes, we will determine if over-expression is due to gene amplification. Given the important role of CKS1B in controlling mitosis and the emerging role of D-type cyclins in myelomagenesis, this gene represents a strong candidate for a gene whose over-expression, possibly as a result of gene amplification, may impart a highly aggressive phenotype on malignant plasma cells.