Chemotherapeutic Studies with Transplants of Spontaneous Mammary Tumors of Mice Growing in Various Hosts*

We have recently reported (8) a comparative study of the effects of chemotherapeutic agents in spontaneous mammary tumors of mice and in firstand second-generation transplants of these tumors. In these studies Z backcross (ZBC) mice were employed as the recipients for the trans plants. It was found that the growth of the spon taneous tumors per se was not inhibited by four of the five agents which had been most effective in inhibiting the growth of the transplants, nor was the survival time of the spontaneous tumor-bear ing mice increased in any instance. The fifth com pound did inhibit the growth of the spontaneous tumors in two of the three trials, but survival time was not increased. We were cognizant that the greater susceptibility of the transplants could, in theory, have been due to some immunogenetic influence of the backcross hosts. It therefore seemed worth while to determine whether similar chemotherapeutic responses could be obtained with transplants growing in the inbred strain of origin, that is, with conditions under which tumors and hosts could in theory be considered genically identical. We have also previously reported chemothera peutic assays with 26 agents in firstand secondgeneration transplants (7). In those studies trans plantations of spontaneous tumors arising in A, C (Bagg albino), or Z (Bittner C3H) strain mice were made respectively into ABC, CBC, or ZBC mice. No definitive data were offered regarding the com parative responses of the transplanted tumors which had originated in different strains of mice. Such comparisons will be presented herein.