Cancer cells have been demonstrated in the blood of man and of animals; they have been demonstrated in the blood of veins draining the tumors,11 and in the peripheral circulation. Among pioneers in this field are Ashworth,6 Engell,14 Pool and Dunlop,28 Roberts et al,29,30 and many others. A most significant and interesting phenomenon occurring following the development of neoplasia in the hosts is the transport and the lodgement of cancer cells, many of which grow into metastases. Thus the invasion or intravasation of neoplastic cells into blood vessels, or both, is followed by their transport into blood vessels via established vascular pathways.
The cell or cells lodge in the capillaries where they become entrapped in an intravascular microcoagula. This is followed, sometimes in a matter of minutes, by the growth and migration of the cells through the wall of the capillaries to the extravascular space,