[Application to chemosensitivity tests of the human tumor-nude mouse system and subrenal capsule assay system]

Since 1974, approximately 200 fresh cancer tissues obtained from various types of cancer patients were inoculated into athymic BALB/c nude mice, of which 30 percent were taken and grown in the subcutaneous space of mice. Among them 15 lines of gastrointestinal and breast cancer xenografts were selected for experimental single agent chemotherapy. The response rates of 14 drugs examined in this xenograft system were compared with the cumulative clinical response rate of each drug in the same type of cancer. Drugs which were clinically effective against one type of tumor were found to be also effective against the corresponding xenograft in nude mice. Thus the human cancer-nude mouse system was considered useful as a predictive secondary screening method for new drugs. This evidence suggested to us the feasibility of utilizing the system as a chemosensitivity test for determining the drugs effective for an individual human malignancy. In our present study, the responses to 15 experimental chemotherapies with single agent or drug combination of 11 lines of cancer xenografts in nude mice were directly compared with the clinical response in each donor patient to the corresponding chemotherapy. Good correlation was obtained between these respective results, the overall predictive accuracy of the experimental results being 93%. Therefore, if the rate of transplantability to nude mice were to be improved, this nude mouse system would become a promising tool for the individual chemosensitivity test. The subrenal capsule (SRC) assay recently introduced by Bogden and his colleagues has excited much attention among Japanese clinical oncologists. In our study, cancer tissues implanted under the renal capsule 6 days after inoculation, did not show marked proliferation and a high percentage of implants was almost replaced by host reactive tissue. It therefore seems necessary to solve some fundamental problems before we can apply this assay method to clinical chemosensitivity trial.