Hormonally responsive versus unresponsive progression of prostatic cancer to antiandrogen therapy as studied with the Dunning R-3327-AT and -G rat adenocarcinomas

Abstract

The present study has compared the response to antiandrogen therapy of the serially transplantable Dunning R-3327-AT (hereafter called AT) versus Dunning R-3327-G (hereafter called G) rat prostatic adenocarcinoma. Castration or chemical antiandrogen therapy (i.e., cyproterone acetate and diethylstilbestrol) of rats bearing established AT or G tumors results in neither regression of tumor volume nor a cessation of the continuous growth of either tumor. By these criteria, both the AT and G tumors progress following antiandrogen therapy. For the AT tumor, this progression is completely unresponsive to hormonal therapy, and thus such therapy does not increase survival of AT tumor-bearing rats. The AT tumor is therefore an example of hormonally unresponsive progression. In direct contrast, while the G tumor likewise progresses following antiandrogen therapy, this therapy does induce a 1.8-fold decrease in the subsequent growth rate of the G tumor. This positive response during progression of the G tumor results in a 78% increase in the survival of G tumor-bearing rats treated with antiandrogen therapy. The G tumor is therefore an example of hormonally responsive progression. These results indicate neither that prostatic cancers which do not regress or cease growing following antiandrogen therapy can necessarily be considered hormonally unresponsive nor that antiandrogen therapy of such tumors has been completely ineffective, since, as shown in the present study, such progression can be of either a hormonally unresponsive or a responsive type. Regardless of which type of progression occurs, however, additional therapy is required to further increase survival. The present study demonstrates that such additional therapy should probably not include the subsequent use of pharmacological doses of exogenous androgen, since, depending on the type of progression, such treatments can actually decrease survival.