Promotion of experimental liver metastasis by tumor necrosis factor

Models for experimental metastasis were established to investigate the influence of rmTNF on tumor‐colony formation in the liver. Highly metastatic lymphoma tumor cells were either injected i.v. or inoculated s.c. to form spontaneous metastases. In both systems, administration of rmTNF to the animals led to significant enhancement of the number of liver metastases in comparison with control groups. The number of metastatic tumor‐cell colonies at an early stage of metastasis was increased, as well as the number of surface metastases in a late stage. Consequently, TNF‐treated animals revealed a higher mortality. The optimal time for TNF to exert this metastasis‐enhancing effect was found to be 7 days after tumor inoculation, In vitro adhesion of the lymphoma tumor cells to a mouse endothelioma cell line was strongly inhibited by monoclonal antibodies interfering with the interaction of VCAM‐1 with VLA‐4. These results support and extend earlier results with a fibrosarcoma lung colonization model. In addition, they show that stimulation of the immune system in tumor‐bearing hosts activates tumor‐promoting pathways, in addition to having possible beneficial effects.