Ultrastructural studies on the lung colonization by nonmetastatic rat tumor cells.

The events during the settlement of BSp73AS (AS) tumor cells in the syngeneic rat lung are described. Although AS cells show highly invasive behavior in vitro, subcutaneous primary tumors grow solidly without detectable metastatic spreading. However, AS cells when applied to the syngeneic rats via the tail vein give rise to lung colonies which grow rapidly at the site of the cells' primary arrest in the capillaries. The colonization comprises formation of microemboli, penetration of the endothelium including the basal lamina, and invasion of the lung tissue. Within two weeks, large colonies develop, thereby compressing, invading, and destroying their surroundings without detectable preference in direction. This establishment of AS tumors in the lung reflects the high invasive potential of AS cells and displays many of the morphological features observed during the formation of colonies of metastatic cell lines. Thus, we conclude that a nonmetastatic tumor cell line, such as AS, may possess almost the whole set of properties necessary for successful metastasis.