HETEROGENEITY OF CANCER CELL POPULATION WITH RESPECT TO NATURAL DRUG RESISTANCE OF CONSTITUENT CELLS

Studies were made, employing 3 different transplant strains of the rat ascites hepatoma, in order to demonstrate the natural resistance of their constituent cells to nitrogen mustard N-oxide after establishing numbers of clonal tumor cell populations from these three ascites hepatomas. Data so far obtained indicate the following facts: (1) A tumor is not a homogeneous constitution but is a mosaic complex of cells with different grades of drug resistance. The natural drug resistance of a tumor cell population is, therefore, the averaged sum of that of all its constituents which differ from each other in their grade of resistance. (2) The grade of natural drug resistance of a whole tumor as well as its constituents is not a fixed one but it can naturally fluctuate around a certain level with a range corresponding to the range of variations of cells in the population.