When Studying Endostatin,why Did Boehm Et Al

When studying endostatin,why did Boehm et al.induce cancer in mice by injecting cancer cells,instead of just doing the experiment on isolated cancer cells in culture?

A) Oncogenes are only active in whole tumors.
B) Tumor suppressors are only active in whole tumors.
C) Cancer cells can go through angiogenesis in culture.
D) Cancer cells cannot be grown outside of the body in culture.
E) Angiogenesis involves multiple tissues in a whole organism.