In vitro and in vivo selection of two Lewis lung carcinoma cell lines.

Two tumor cell lines adapted to grow in vitro were originated from an explant of lung metastases of Lewis lung carcinoma. These lines differ in their malignancy when reinoculated into syngeneic animals; nevertheless, they do not show any difference for their in vitro clonogenic ability. From these lines 2 in vivo sublines of 3LL carcinoma were developed. The TD50 of the 2 in vivo sublines are different, and both the values obtained are lower than that of the original line. These results are interpreted as a selection of more malignant tumor cell lines.