Comparison of the expression levels of five genes according to five subtypes in the microarray data sets. (A) Proportion of five breast cancer subtypes in two large-sized microarray data sets. (B) Expression levels of the five markers according to the subtypes in Vijver et al. (C) Expression levels of the five markers according to the subtypes in Wang et al. Distribution of expression levels of each marker was described with box plots. The bottom and top of the box are the 25th and 75th percentile, and the band near the middle of the box is the 50th percentile.