Vascular permeability in malignant disease.

Experimental demonstration that vessels draining large tumours are impermeable to cellular elements. Thus the pulmonary vessels of animals bearing large, primary (other than gastro-intestinal) cancers can become impermeable to tumour emboli. This imperviousness prevents the establishment of secondaries in the lung and promotes the transpulmonary passage of tumor cells. This phenomenon may account for the development of paradoxical metastases.