Histologic and metastatic properties of the patient-derived orthotopic breast tumor xenografts. (A) For the HT17 and HT39 patient tumors, representative images are shown here of (from left to right) primary tumor from the patient of origin (H&E), primary tumor in the xenograft (H&E), and staining of the xenograft tumor with a human-specific anti-cytokeratin antibody (immunohistochemistry, brown). Magnification ×40. (B) In vivo invasion assay for HT17 and HT39 xenograft tumors to an EGF gradient, passages 1 through 4 (P1-P4). Invasion to a gradient of serum (FBS) showed similar results. The number of migratory cells remains similar over passages (P = 0.47 for HT17, P = 0.82 for HT39, by one-way ANOVA). Results are plotted as average number of cells per microneedle. Error bars: SEM, n ≥ 5 mice. (C) Representative images of spontaneous lung metastasis of the xenograft orthotopic tumors (H&E). Magnification ×40.