[Chemical carcinogenesis in tissue culture: criteria and transformation tests]

We belive that there are four criteria for the evaluation of cell transformation in culture: development of transformed colonies, appearance of altered foci when cells sensitive to contact inhibition are used, formation of colonies in agar, and the capacity to induce tumors in animals (tumorigenic potentiality). The formation of transfomred colonies provides a short term (t. of BERWALD-SACHS) to determine the transformating activity of chemical carcinogens. Judging by the published results there is a good correlation between this in vitro test and in vivo results. Nevertheless this test does not seem to me appropriate to studies on the activity of complex mixtures. But the use of a short term test to monitor transformation in the course of long term tests does seem justified and useful. The formation of altered foci is the basis of two intermediate term tests (t. of CHEN-HEIDELBERGER, and t. of HUEBNER'S group). The value of these two tests have been experimentally proven, but their only disadvantage is the necessity of using cells that are not readily available. Formation of colonies in agar is a criterion useful only for the control of cell transformation during long term tests. Tumorigenicity constitutes a long term test. It is the absolute proof of cell transformation. We propose a long term experimental system combined with periodic checks of transformation by cell cloning in liquid medium (criteria of the transformed colonies or altered foci), and by cloning in agar. The reported results show that it is possible to determine cellular transformation accurately without recourse to the animal. This combined long term test permits the classification of treatments based on their transformating capacity.