Effect of host age on tumor-associated angiogenesis in mice.

Previous reports on the slower growth of tumors in senescent mice have suggested a decrease in tumor angiogenesis in these animals, but such an observation has not yet been documented quantitatively. In this study, we report the relative amount of tumor angiogenesis and tumor volume for two different types of tumor in 11 young (8-9-wk old) versus nine older (19-mo old) male C57BL/10 mice. B16 melanoma or SP1 methylcholanthrene-induced fibrosarcoma cells were injected into the ventral skin of mice. After 3 days, the mice were killed and the injection sites were examined for angiogenesis surrounding the tumor (centrally directed tumor angiogenesis), nerve-associated angiogenesis, and tumor volume. In the older mice, there was significantly less centrally directed tumor angiogenesis for both tumors tested, and nerve-associated angiogenesis was decreased for B16 melanoma. The mean tumor volume for the B16 implants was smaller for the older animals, but the mean SP1 tumor volumes were identical for both age groups. These findings support the hypothesis that tumor growth in older animals is associated with less formation of new blood vessels, and this may explain the slower tumor growth observed in aged animals with certain experimental tumors.