Unsupervised clustering of genome-wide expression profiles of PCNSL and non-CNS nodal and extranodal DLBCL. The gene list used was approximately 11 500 in number (genes present on at least 35 of the 43 arrays). The metric used was “standard correlation” in GeneSpring. Because the 2-color array method involved a reference standard, the colors do not represent actual gene expression levels in the tumor samples but rather the ratio of the tumor mRNA to the reference mRNA. The LOWESS method of normalization was used. To the right of the cluster are shown 10 genes of interest enlarged from the cluster; the colored bars correspond to the 3 phenotypes identified at the bottom of the cluster (“Brain,” “Extranodal,” and “Nodal”; left to right). SPP1 (osteopontin), CHI3L1 (chitinase-3 like 1), IRF4 (MUM1), S-100B (S-100 calcium binding protein beta), SERPINA3 (serine proteinase inhibitor, clade A, member 3), CRYAB (crystallin alpha B), LUM (lumican), COL1A2 (collagen type 1 alpha 2), COL6A1 (collagen type 6 alpha 1), and LAMA4 (laminin alpha 4).