[Usefulness of LDH isozyme for monitoring the therapy of human breast cancer transplanted in nude mice].

Human breast cancer (Br-13) serially transplanted in nude mice in ascitic form was used in this experiment. Released isozyme of human lactate dehydrogenase (LDH) was detected in the blood of the Br-13 tumor-bearing nude mice, and the serum levels of the isozyme rose associated with the increase of neoplastic cell number in ascitic fluid. After Br-13 bearing nude mice were treated with single drug or a combination of cyclophosphamide, adriamycin and 5-fluorouracil, serum LDH levels were monitored and compared with the change of ascitic cells. When effective treatment was performed, serum LDH-5 levels increased transitorily 1 or 2 days after drug administration, then decreased and became undetectable. These changes indicate a good correlation with the extent of the cell damage and the increase of life span of the mice. In conclusion, monitoring of human LDH isozyme in serum of nude mice was a useful marker for evaluating the efficacy of experimental chemotherapy in nude mice.