The growth of a patient mesothelioma xenograft was supported by development of a murine vascular network. A patient mesothelioma was implanted in a cohort of mice and monitored for tumor growth. Once tumors began to actively grow, representative tumors were resected at weekly intervals and analyzed for vessel content. Staining for huCD31 was prominent in the original patient specimen (A), much reduced at 4 weeks (B) and negligible at 9 weeks (C). In contrast, patient specimens were not stained for msCD34 (D), whereas at 4 weeks large numbers of vessels stained for msCD34 (E) and by 9 weeks, msCD34 labeled vessels were predominant (F). The graph (G) summarizes the loss of detectable human vessels and acquisition of murine vessels over a 9 week period. (bars = 100 μ).