Experimental Chemotherapy in Chemically Induced Mouse Tumors and Their Transplants^*

Uniform subcutaneous fibrosarcomas can be induced by single injections of 3,4,9,10-dibenzpyrene into C57BL/6 mice at the rate of 200–300 tumors per week from a colony of approximately 3,000 animals (8) and are practical for chemotherapy screening as shown by their response to five different chemotherapeutic agents previously tested in transplanted tumors. The animals are safe, since no carcinogen is excreted. Histology showed more marked responses (reduced mitoses, fibrosis) in induced than in transplanted tumors. Chemotherapy with thioTEPA administered during the induction period or latent phase caused significant delays in the appearance of tumors, which is analogous to the tumor-inhibiting effect claimed clinically for thioTEPA when administered after radical surgery for breast cancer.