[The rate of in vivo selection of highly metastatic and resistance-inhibiting variants of tumor cells].

The rate of in vivo selection of tumour cells of STHE strain (spontaneously transformed in vitro hamster embryo cells, previously not selected in vivo) after their intravenous inoculation to normal Syrian hamsters was studied. At different time intervals after inoculation tumour cells were isolated from the lung tissue of individual animals, cultured in vitro and the their metastatic activity (MA) and natural resistance-depressing activity (RDA) were studied. It was demonstrated that selection of highly metastatic variants of tumour cells begins immediately after inoculation; on days 5-6 after inoculation the presence of such variants is observed in the majority of animals. Selection of resistance-depressing variants of tumour cells (determined in a less sensitive test) was first noticed on days 9-10 after inoculation of tumour cells. The correlation between MA and RDA of tumour cells was observed. The data obtained give evidence in favour of preexistence of genetic MA and RDA variants of tumour cells in the original population of tumour cells.