Gene array analysis demonstrates the differences between normal and malignant PCs. (A) “Filter gene” function within dChip identified 125 genes with a large variation across samples (filtering criteria: [1.10 < SD/mean between < 10.00] P call % in the array used, 20% or greater). Unsupervised clustering using this list separates the samples into 2 trees: normal samples in one tree versus MGUS and MM samples in the other. The second tree further separates into 2 branches, one containing mainly MM samples and the other containing mainly MGUS samples. (B) To identify specific genes differentially expressed between N and MGUS, arrays were grouped according to sample type, and their mean expression levels were compared using the dChip compare samples facility (criteria, lower bound -fold change [E/B > 1.1] or [B/E > 1.3], mean difference [E - B > 50] or [B - E > 150], t test P < .05). Two hundred sixty-three genes were identified, most of which were down-regulated. (C) Using this gene list to hierarchically cluster all the samples defines 2 branches: one contains the N samples, and the other contains MGUS and MM samples.