[Electron microscopic study on the method of evaluation of SRC assay]

The subrenal capsule assay (SRC) is a rapid and precise method for evaluation of chemotherapeutic agents. However, it seems to present some difficulties with regard to sensitivity, since evaluation is done by measurement of graft size. In this study, SRC was performed on six clinical cases of colorectal cancer using nude mice, which were given UFT 15 or 20 mg/kg orally or 2.5 mg/kg CDDP subcutaneously for 2-6 days. Histological changes in the grafted tumors were then observed by electron microscopy. Mucous granules and other features were assessed for evaluation of assay sensitivity. The number of mucous granules seemed to be the most reliable parameter that paralleled the sensitivity evaluated by tumor diameter. Other features such as nuclear mitosis, lysosomal increment and abnormal accumulation of ribosomes, had little correlation with sensitivity. However, further exploration is warranted with regard to local defects of the cytoplasm. This ultrastructural examination suggested that grafted tumor cells were damaged slightly by implantation under the renal capsule, and that the SRC using tumor size as a parameter is clinically useful under conditions where the tumor xenografts show good viability and proliferation in the control group.