The growth of primary subcutaneous fibrosarcoma and its pulmonary metastases in normal and athymic Swiss mice.

The growth of primary subcutaneous fibrosarcomas and their pulmonary metastases was studied in normal and athymic Swiss mice. The metastases tended to develop more rapidly than did the primary tumors. However, when growth rates of tumors of small volumes (up to 1 cm3) were compared, the tumor and metastases exhibited similar rates of development in both strains indicating the growth rate of pulmonary metastases was related to that of the tumor of origin. Modified immune reactivity, as in athymic mice, influenced the growth of the same tumor in that the subcutaneous fibrosarcoma exhibited a faster rate of development, while the growth rate of pulmonary metastases decreased, when compared with growth in Swiss mice. Therefore, it appears that growth characteristics of the primary tumor from which metastases originated and the reactivity of the host must be included among the factors determining metastatic growth rates.