Similar gene expression profiles displayed by different activating signals. Nonvariable common genes among phenotypic classes were determined using a variance test (10% level) in combination with the parametric t test and nonparametric Kruskal-Wallis test (P < .001). Data were visualized using Cluster/Tree View. Stroma 1-3, normal stroma-treated samples; stroma 4-5, MM stroma-treated samples. (A) Genes shared by all 3 treatments when compared to NIL controls; 347 genes were found to be commonly expressed by IL-6, stroma, and N-ras samples and not by NIL controls (left). Functional characterization of these common genes indicates that metabolic genes are the most represented functional group (right). (B) Genes expressed similarly by IL-6 and N-ras samples but different from stroma and NIL samples; 114 genes were shared by IL-6 and N-ras samples but different from stroma and NIL samples (left). Most of these genes encode translation proteins (right). (C) Genes shared by IL-6- and stroma-treated samples but different from NIL and N-ras samples; 169 genes were shared by IL-6- and stroma-treated samples but not by NIL and N-ras samples (left). Most of these were cell cycle genes (right).