Supervised classification of 12 paired lymphoma samples (training series). (A) Correlation plot of the FL stratification profile. Correlation of the expression profile of each tumor sample with the average expression profile of all indolent samples is depicted on the horizontal axis, and the correlation of the expression profile of each tumor with the average expression profile of all aggressive tumor samples is shown on the vertical axis. Tumors classified above the threshold are classified as molecular high-grade; tumors below the threshold are classified as molecular low-grade. (B) Expression data matrix of 81 marker genes from tumors of the indolent as well as the aggressive phase of 12 patients with FL. Each row represents a tumor and each column a gene. Genes are ordered on the basis of their SNR. Tumors are rank ordered according to the difference in correlation with the average high-grade profile and the correlation with the low-grade profile (middle panel). The solid yellow line is the classifier with optimal accuracy; patients above the yellow line have an aggressive disease course; below the yellow line, they have an indolent disease course at the disease episode at the time of biopsy. Selected clinical data are shown in the right panel. For morphologic data, □ indicates FL grade 1 or 2; ▪ indicates FL grade 3b or DLBCL. IPI scores and clinical behavior at time of biopsy are as described in Figure 1.