Experimental chemotherapy studies: intercomparison of assays

In a limited number of experimental tumour systems the response to chemotherapy has been measured in terms of both cell survival and tumour growth delay. Both of these endpoints have complicating factors which lead to problems in interpretation of results. The time after drug administration at which cell survival is measured can be of predominant importance. If the time is too short, drug action may be incomplete and recovery from potentially lethal damage may still be occurring. If the time is too long, proliferation of surviving clonogenic cells may have begun. Tumour growth delay on the other hand is likely to be influenced by the effect of the chemotherapy on the host, as well as on the tumour. This may be particularly important when the tumour is significantly immunogenic. The rate of regenerative proliferation of the surviving clonogenic cells can be different following treatment with different cytotoxic drugs, hence resulting in different periods of growth delay from the same initial level of cell killing. Also some agents appear to be significantly cytostatic, producing considerable growth delay in the absence of cell killing. New data are also presented for the RIF-1 tumour and for multicellular tumour spheroids of the EMT6/Ca/VJAC line.