Gene expression analysis by Affymetrix GeneChip probe arrays. A, Variation of gene expression between the primary HBC-12B tumor and the corresponding xenograft. Scatter plot representing the gene expression of 29,683 probe sets (primary tumor versus xenograft p3). red dot, probe sets with high residual values. B, Variation of gene expression between xenograft at passage 3 and passage 6. C, Number of overexpressed (red) and underexpressed (green) genes between patient tumor/xenograft pairs HBC, human breast cancer; HBC-n, HBC primary tumor n; HBCx-n, HBC xenograft tumor n.