What Is the Evidence That Tumors Are Angiogenesis Dependent?

In this issue of the journal, Kreisle and associates (/) report that angiogenesis and growth of B16 melanoma decreased with age in C57BL/10 mice. They suggest that age-related reductions in tumor growth may be secondary to a dimin-ished neovascular response by the host. In another mouse tumor system (SP1 fibrosarcoma), in which tumor growth did not decline with age, the overall neovascular reaction elicited by the tumor from the host was sufficient to sup-port the growing tumor. However, the new vessels in the old mice arose mainly from peripheral nerves, whereas in younger mice, they arose from subcutaneous tissue. The behavior of tumors in both systems is consistent with the concept that tumor growth is angiogenesis dependent (2). This hypothesis, which was first proposed in 1971, can be stated in its simplest terms: Once tumor take has oc-