Clonal variation in the arrest, survival and growth of RIF-1 mouse sarcoma cells in the lungs of C3H mice.

The relationship between the long term retention of 125IUdR-labelled tumour cells in the lungs and the formation of pulmonary lesions, has been examined for six in vitro isolated RIF-1 clones. Following i.v. injection, the initial number of cells trapped in the lungs was close to 100% in all cases. However, the rates at which individual clones were subsequently cleared from the lungs and the fraction of persistently retained cells varied considerably. Whilst clones also differed markedly in their lung colony formation efficiency (L.C.F.E.) there was no clear correlation between the long term retention of tumour cells in the lungs and subsequent metastasis formation, even when the retention of one clone was artificially increased in the lungs by admixture with microspheres. The fate after injection of clone 16 which is retained well in the lungs but which is of low L.C.F.E. has been compared with that of clone 19 which is retained poorly in the lung but which is of high L.C.F.E., using in vitro clonogenic capacity as a measure of cell viability in the lungs. Our findings show that clone 16 cells arrested in the lungs are in a viable, albeit "dormant", state some 26 days post i.v. injection. In contrast, arrested clone 19 cells proliferate rapidly in the lungs. These data may indicate varying significance of tumour cell and host properties in the metastatic success or failure of individual RIF-1 clones.