Venous diversion trapping and growth of blood-borne cancer cells en route to the lungs.

A proportion of W-256 tumour cells injected intravenously into a tail vein of the rat are diverted into venous plexuses en route to the lungs; here tumour cells remain trapped, proliferate and form invasive solid tumours in the pelvis and hindquarters, which cause paraplegia, metastases and death. Also, cells trapped in veins produce tumour nodules distributed along the length of the tail; this effect in markedly enhanced by temporarily arresting the outflow of blood from the tail for a few seconds only immediately after cells are injected. Continous monitoring of the radioactive signal over the lungs after W-256 cells labelled with 125IUDR were injected showed that massaging the tail or intravenously injecting isotonic saline into the tail dislodged cells trapped in veins. In heparinized rats, tail trapping was markedly reduced, although not entirely abolished, and venous trapping in vertebral and pravertebral regions was decreased. The anatomical distribution of growth of the trapped cells in rats closely resembled metastases involving dissemination via the "vertebral venous system" produced by certain cancers in man. Labelled tumour cells trapped in the lungs of untreated mature rats commenced dying rapidly in situ wiht 1-2 h after injection; the majority had disappeared within 24 h, and less than 1% of the injected tumour cells survived to form lung colonies. Experimental evidence is presented which indicates that the lungs play a vital role in rapidly eliminating a high proportion of blood-borne cancer cells in the adult individual.