Some Observations on the Use of Transplanted Tumors in Radiobiological Research

The successful transplantation of a tumor from one rat to another was reported by Hanau in 1889 (1), and by the turn of the century transplanted tumors were being used for radiation experiments. Since that time, experimentalists in this field have become increasingly critical of the material which they have been using. In the early days workers were satisfied if they obtained some takes with transplanted tumors; they did not worry much if the percentage of takes was low, or if spontaneous regressions were frequent. Gradually, it was recognized that experimental tumors which behaved in this way were so unlike human cancer that results obtained with them could not be extrapolated to the naturally occurring disease. Francis Carter Wood criticized this early work very strongly in 1931 (2). Unfortunately even he was not sufficiently critical, for he recommended the use of sarcoma 180, on the ground that mice could not be immunized against it. Only one year later Andervont (3) showed that mice could be immunized against this tumor also. Whether or not human tumors give rise to an immune reaction is still being debated (4), but it appears unlikely that host resistance plays an important part in the cure of a human tumor (5, 6), although many clinicians take the contrary view. This article is based on the standpoint that immunological differences between tumor and host, if present, are of only minor significance in human cancer (with the exception of chorionepithelioma, where such differences between tumor and host are to be expected). The occasional spontaneous regression of a human cancer (7) cannot be adduced as conclusive evidence of such immunity, since the same result would follow from a change in the hormonal status of a host bearing a hormone-dependent tumor. In general, therefore, it may be said that a transplanted tumor in animals which arouses intense and easily demonstrable immunity is not necessarily a good model of the human disease. An immense step forward was made when inbred lines of mice become available,