Heterogeneity of the Growth and Metastatic Behavior of Cloned Cell Lines Derived from a Primary Rhabdomyosarcoma1

In order to study the heterogeneity of the metastatic and tumorigenic behaviors of malignant neoplasms, we have iso lated a series of cloned cell lines from a primary nickel-induced rat rhabdomyosarcoma. The growth characteristics in vitro and in vivo and metastatic capacity following s.c. or i.v. injection of cells were compared to those of the parental cell line. Differ ences between the cloned cell lines themselves and between the clones and the parental cells were found in the number of métastases provoked by both i.v. and s.c. injections, in the number of cells required to induce s.c. tumors, and in the growth rate of those tumors. In vitro, the doubling times and saturation densities of the different cell lines varied greatly. A direct correlation was observed between the 50% tumoral dose and the initial tumor growth phase. We found that there was a tendency for lines which were highly metastatic after s.c. injection to have a low metastatic capacity after i.v. injection and inversely. The two types of metastasis (spontaneous and experimental) appear therefore to depend on different char acteristics of the cells used.