Sample relationships are influenced by clinical and gene-expression characteristics. Two hundred sixty-four myeloma patient samples and 6 normal plasma cell control samples were subject to unsupervised hierarchical clustering based on 9174 differentially expressed probe sets. Highly related branches (labeled groups 1-5) were identified by setting a fixed similarity metric (GeneMaths software; Applied Maths, Austin, TX) and requiring at least 12 samples for membership; unlabeled samples comprise various smaller groups. (A) Patient attributes are encoded below the sample dendrogram. Attributes with nonrandom distribution (P < .05) are indicated by asterisks. Black is associated with age older than 60 years, female sex, IgG isotype, 1 or 2 prior therapies, hybridization batch 1 (trials 024, 025, and 040), and low purity score. White is associated with age 60 years and younger, male sex, other isotypes, 3 or more prior therapies, hybridization batch 2 (trial 039), and high purity score. (B) An overview of the 9174 differentially expressed probe sets, with an expansion of specific functional groups.