Pretreating mice with chemotherapy can enhance metastasis formation in the lungs of mice. Daenen and colleagues and Gingis-Velitski and colleagues report that chemotherapy has effects on the microenvironment that account for these protumorigenic effects. Expression of vascular endothelial growth factor receptor 1 (VEGFR-1) is enhanced on a subset of endothelial cells in the lungs of mice following chemotherapy exposure. On the cover, mouse lung endothelial cells after cisplatin pretreatment are shown, characterized by CD31 expression (red) and VEGFR-1 expression (green). Knowledge of the host effects induced by chemotherapy may facilitate strategies to improve therapy efficacy. For details, see the article by Daenen and colleagues on page 6976 and the article by Gingis-Velitski and colleagues on page 6986 of this issue.