Macrophage content of metastatic and nonmetastatic rodent neoplasms

In this study, we have examined the macrophage content of 16 different rodent tumors and failed to demonstrate a correlation between the extent of macrophage infiltration into neoplasms and the metastatic behavior of the tumor. We also did not find a correlation between the macrophage content of ultraviolet radiation- (UV) induced murine fibrosarcomas growing in normal or UV-irradiated syngeneic mice and the immunogenic potential of the tumor. After s.c. inoculation of single viable cells, tumors with a high level of infiltrating macrophages required a longer induction period to form palpable tumors than tumors with low macrophage content. The macrophage content of neoplasms also did not correlate with in vitro or in vivo growth rates. We conclude that no generalizations can be drawn regarding the relationship between macrophage content of neoplasms and their metastatic potential.