The role of microvascular environment in the metastasizing ability of an experimental tumor.

A rapidly growing, locally very invasive and easily transplantable fibrosarcoma that was developed through chemical carcinogenesis in Balb/c mice in this laboratory several years ago did not metastasize into the viscera of its hosts when implanted into the subcutaneous connective tissue or skeletal muscle of syngeneic mice. When, however the same tumour was implanted into the liver or the kidneys of Balb/c mice it metastasized extensively into many different organs within 2 weeks of its transplantation. Evidence is presented that because of some unknown deficiency the cells of the fibrosarcoma under study are unable to penetrate through the endothelial wall into the lumen of the particular type of vessels which surround and vascularize the tumours in the subcutaneous connective tissue and muscle, and that, in contrast, they can easily cross into the lumen of the vessels that surround and vascularize them in the liver and kidney. Thus, this in vivo study indicates that the type of microvascular environment in which certain experimental tumours are transplanted can control their ability to accomplish vascular invasion, the first step of the metastatic process.