Effects of sorafenib on A673 xenografts in vivo. A. Schema depicts experimental design in vivo. Sarcoma cells were infused by tail vein on day 0. Xenografts were allowed to develop for 21 days, and mice were then randomized to i.p. injections of placebo versus sorafenib (75 mg/kg) x 21 days (or until tumor harvest). B. Mice treated with sorafenib survived significantly longer than placebo-treated mice (median survival post-treatment 29 days vs. 18 days, P = 0.03 by log-rank test). C. Sorafenib-treated metastatic lung tumors demonstrated significantly greater tumor necrosis than placebo-treated tumors at indicated time points (P < 0.001 by paired t-test at both time points). D. Representative images of placebo- and sorafenib-treated tumors stained with hematoxylin and eosin (H&E) on treatment day 12. Placebo-treated tumors remain highly cellular and mitotically active with minimal tumor necrosis, while sorafenib-treated tumors show necrosis (**) and inflammation (*) surrounding areas of viable tumor. E. Sorafenib-treated metastatic lung tumors demonstrated significantly decreased numbers of Ki67 positive cells than placebo-treated tumors at day 7 and day 12 of treatment (P < 0.001 by paired t-test at both time points). F. Representative images of placebo- and sorafenib-treated tumors stained for Ki67 on treatment day 7. Non-necrotic, viable areas of sorafenib-treated tumors demonstrate fewer proliferating cells than placebo-treated tumors. Boxed areas are depicted at higher magnification. G – H. Metastatic lung tumors harvested at indicated time points demonstrate statistically greater ALDHbright CSCs than placebo-treated controls (P < 0.001 by paired t-test). For all panels, representative data from 2 – 3 experiments are shown.