Ploidy distribution of tumour cells derived from induced and spontaneously arising metastases of a murine radiation-induced sarcoma, RIF-1.

Flow cytometric analysis of the X-radiation-induced sarcoma RIF-1 has shown that the parent tumour is composed of diploid and tetraploid subpopulations of cells, each capable of independent proliferation. We have now examined artificially induced and spontaneously arising metastases of the RIF-1 tumour and have found in both cases that, unlike the parent tumour from which they are derived, they exhibit a single level of ploidy which is stable throughout successive in vivo and in vitro passaging. This finding suggests that at least in this tumour system metastasis is a clonal event.