Hierarchical clustering analysis of the differentially expressed genes in disease progression. The differentially expressed genes analyzed by hierarchical clustering method in disease progression. The genes were classified into three major clusters by visual inspection. Clustering method: Average linking; Similarity measure: Euclidean distance. Samples are displayed in columns and genes in rows. Gene expression is represented as a color, normalized across each row, with brighter red for higher values and brighter green for lower values. N (Normal control group), Int (intermediate lesions group), Ad (advanced lesions group). The list of differentially expressed genes in disease progression is provided [see Additional file 8].