Unsupervised clustering of 72 FL samples, grades 1, 2, and 3, shows a relative biologic homogeneity of FL. There is a separation in 3 main groups with no enrichment for morphologic grades or clinical behavior in either of the groups. Each row represents a tumor and each column a single gene. Gene expression is depicted according to the color bar. Red indicates a high level of mRNA expression relative to the reference and green indicates a low level of expression. Selected morphologic and clinical data are depicted in the right panel. For clinical features, □ indicates indolent and ▪ indicates aggressive disease behavior (Table 1 lists criteria). For morphologic grading, □ indicates grade 1; ▨, grade 2; and ▪, grade 3. For IPI, □ denotes scores 0, 1, or 2, and ▪, 3, 4, or 5. ▦ denotes insufficient data.