Cell lines were obtained from nine individual spontaneous metastases of the murine mFS6 sarcoma by s.c. inoculation of lung deposits in syngeneic mice. When inoculated i.m., two lines (M4 and M7) from metastases had greater, and two (M8 and M9) had less metastasizing capacity than the primary mFS6 sarcoma. The remaining cell lines gave spontaneous metastases similar in incidence, number and weight to the primary mFS6 tumor. When inoculated i.v., M2 and M4 gave consistently more lung deposits than mFS6 cells, whereas cells from M1, M5, M6 and M8 produced fewer artificial metastases than the primary tumor. Eight individual lung metastases were disaggregated and tested for metastasizing capacity immediately after isolation from the lung parenchyma: spontaneous and artificial metastases from metastatic cells were similar to the primary tumor, except for one secondary which was less metastatic. The immunological characteristics of cell lines from metastases were studied by in vivo immunization and challenge. Seven lines from metastases and the primary tumor had weak cross-reacting transplantation antigens whereas two lines (M3 and M4) had no demonstrable antigenicity. Thus, cell lines from individual spontaneous metastases are heterogeneous in many respects, including metastasizing capacity. However in this model metastasis does not appear to be the expression of strong selection of variant cells with increased metastatic potential.
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