Ridit analysis of the effects of carcinostatic chemicals on the growth indices of the Nelson mouse ascites tumor.

The evaluation of the effects of drugs on the growth of transplanted ascites tumors in laboratory animals can be based on the performance of different growth indices (2). Some of them (e.g., the total number of free tumor cells in the peritoneal cavity, the total packed cell volume) measure directly the increments of the tumor cell number or volume, whereas the other indices (e.g., survival time, body weight) are of an indirect nature, and their usefulness for screening purposes must first be established in an empirical way. In a previous communication (3) the performance of several growth indices of the Nelson mouse ascites tumor growing in untreated mice and in those treated with 6-mercaptopurine has been compared and evaluated by three different statistical procedures. The technic of "ridit analysis" (1) has been found to be particularly useful when a comparison of different growth indices on the same dimensionless scale is desired. Such a technic permits making statements concerning the probability that an animal undergoing treatment A will be better off than an animal undergoing treatment B (which may be: no treatment at all = "negative control," or a treatment with some standard drug = "positive control"). An average ridit has the same interpretation (probability that a treated animal will be better off than a control animal) for all types of indices, which makes the direct comparison of ridits for different indices meaningful. In the present publication, the technic of ridit analysis has been applied to the tumor growth inhibition data collected in the course of two series of experiments in which mice bearing the Nelson mouse ascites tumor in either fluid or solid form have been treated with a selected group of chemicals.