The relationship of embolic homogeneity, number, size and viability to the incidence of experimental metastasis

Abstract

-B 16 melanoma cells grown in vitro were used to study factors influencing experimental metastasis. Groups of C57 BL/6, mice were given intravenous injections of varying numbers of viable B 16 melanoma cells, with or without gamma-irradiated B 16 cells, viable B 16 cells with or without C 57 embryo cells, and equal number of viable B 16 cells suspended singly or in clumps. The data permitted the following conclusions: The number of lung metastases was proportional to the number of viable tumor cells injected i.v. Mice injected with clumps of B 16 tumor cells had a higher number of lung metastases when compared to mice injected with an equal number of single B 16 cells. Mice injected with viable B 16 tumor cells together with dead B 16 cells or viable C 57 embryo cells had a statistically significant higher number of pulmonary tumors as compared to mice injected with viable B 16 cells alone. The mechanism responsible for these phenomena might be the induction of pulmonary vasospasm by arrested emboli bringing about an increased trapping of tumor cells in the lung capillaries. These results point out the absolute necessity for a standardized and homogenous systems for studies of metastasis. In addition, they call attention to the possible role of circulating dead tumor cells in the formation of secondary tumors.