The Growth of the Emt6 Tumour In the Lungs of Balb C Mice Following Intravenous Inoculation of Tumour Cells From Culture

The growth of the EMT6 tumour in the lungs of Balb C mice has been studied following intravenous inoculation of different numbers of tumour cells taken from culture. At various times after injection of cells into mice, cell suspensions have been prepared from pairs of lungs and the number of in vitro colony forming cells assayed by plating into petri dishes. Following intravenous injection of 10 5 cells, the time required for doubling of the number of clonogenic tumour cells appearing in the cell suspension is around 17 hr until such time that the total tumour cell population per set of lungs reaches 10 8 cells (at 10–12 days). This doubling time has to be corrected for changes in ability to extract cells from the lungs into the cell suspension at various times and also for possible changes in plating efficiency in vitro. When these correction factors are applied, the most likely value for the doubling time of clonogenic tumour cells in the lungs is in the range 20–24 hr. This is a similar figure to that previously deduced for the EMT6 flank tumour during its microscopic period of growth. After reaching a total size of 10 8 tumour cells, the time for doubling of the number of clonogenic tumour cells in the lung increases. During the later stages of tumour growth a good correlation is seen between total lung tumour weight and the number of clonogenic cells present. For the final 3–4 days of the initial period of rapid tumour growth, it is possible to carry out a haemocytometer count of tumour cells in the lung suspension and hence surviving fraction experiments may be carried out after various forms of treatment. In this way the response to treatment of microscopic tumour foci may be determined.