The characteristic structural features of the blood vessels of the Lewis lung carcinoma (a light microscopic and scanning electron microscopic study).

Vascular corrosion casts of Lewis lung carcinomas (LLC) grown subcutaneously in C57BL/6-mice are correlated with histological sections and with tumor tissue prepared for scanning electron microscopy (SEM). By making low, medium and high pressure cast preparations we studied the influence of perfusion and injection pressure on the resulting cast sample. Three types of vascular proliferations are distinguishable in LLC: Small globular outgrowths on sinusoidal dilated tumor capillaries, caused by proliferation of their endothelial cells. New sprouts on surrounding host vessels, invading the small, still avascular implant. Superficially located, centrifugally running sprouts in peripheral regions of large tumors. They invade the surrounding host tissue. Vascular sprouts are of venous origin, have a fragmentary endothelium and are rather "leaky" if casted. High pressure preparations of large tumors reveal central avascular cavities surrounded by centripetally running, compressed and blind ending tumor vessels. Irrespective of the applied injection pressure, the casts always exhibit extravasal channels caused by degeneration of the endothelium of central tumor vessels. We show that SEM of vascular corrosion casts combined with histology not only demonstrates such contrary processes as the development of tumor blood vessels and the simultaneously occurring vascular degeneration, but also elucidates all other morphological characteristics of the tumor vascular system.