A. Representative microscopic images of primary cRCC (a, b, c, d) and matched orthotopic xenograft (e, f, g, h) tissues immunostained for various markers (X600 magnification). Ki67 (a and e, case # 2), CAIX (b and f, case # 2), CD10 (c and g, case # 12), and VEGF (d and h, case # 6) stains are shown. B. Examples of species specific labeling of CD34-positive endothelial cells in two representative xenograft cases (X200 magnification). Murine (i) but not residual human (j) endothelial cells are detected in a FNG 4 cRCC graft grown in the host for 2 months (case # 19). Both murine (k) and human (l) endothelial cells are present in a FNG 3 cRCC graft grown in the host for 8 months (case # 9). Black arrows indicate the kidney of the mouse host.