The relationship between tumor size and chemosensitivity of murine bladder cancer

The relationship between tumor size and antitumor efficacy of chemotherapy was quantitated using an i.d. bladder cancer in C3H mice. The fundamental hypothesis was that tumor microenvironmental factors progressively changed with tumor growth, which then influenced the cell killing activity of agents. For all five chemotherapeutic agents examined, the antitumor efficacy progressively decreased as the tumor became larger ("volume effect"). The change in antitumor efficacy was expressed as the treatment delay (days) to cause a 50% reduction in antitumor efficacy (designated as volume effect/50, VE50). The VE50 value of Adriamycin (ADM) was 25.1, cisplatin was 10.4, carboplatin was 5.7, vinblastine was 4.7, and cyclophosphamide (CP) was 3.2 to 4.1 days; indicating the antitumor effect of ADM was least and CP was most influenced by tumor size at the time of treatment.