Patterns of blood-vessel invasion by mammary tumor cells.

Rat mammary tumor TMT-081 was employed as a model for blood vessel invasion because its mode of metastasis resembles that of human tumors. The invasive mechanism was studied with two methods of serial transplantation: transfer of enzymatically dispersed solid tumors, and transfer of buffy coat containing circulating tumor cells. The latter method produced greater invasion of blood vessels, including larger veins and occasionally arteries, perhaps by obviating damage to tumor cells during enzyme treatment. The course of migration was traced by three-dimensional examination in the high voltage electron microscope, as well as the light microscope. Two broad patterns were found for the course of invasion of small and large vessels respectively.