ON THE PRESENCE WITHIN TUMOURS OF CLONES THAT DIFFER IN SENSITIVITY TO CYTOSTATIC DRUGS

Abstract

An in vitro test model was used to study the heterogeneity of tumours with respect to the sensitivity to cytostatic drugs. Methylcholanthrene‐induced sarcomas in mice were used. The effect of the drugs was determined as the reduction of the incorporation of H 3 ‐thymidine into drug‐treated cells compared with control cells. To test the heterogeneity of the tumours, these were cut into four equal parts and each part was tested separately. In some of the tumours, the quarters differed significantly in their sensitivity to the same cytostatic treatment; in others, no such differences could be found. Both primary and serially transplanted tumours were studied. The present method revealed no differences in heterogeneity of the tumours in these two groups. The most likely explanation of these results is that the tumours are built up by different clones with different sensitivity to cytostatic drugs and that different parts of the tumours are different with respect to the distribution of clones.