Prevalence of Measurable Disease in Metastatic Castration-resistant Prostate Cancer

Because of the low historical prevalence of measurable disease in metastatic castration-resistant prostate cancer (mCRPC), phase II trials have used prostate-specific antigen (PSA) and bone scan changes as primary end points. Frequent whole-body imaging and improved computed tomography technology currently identify measurable disease more frequently, warranting consideration of objective response as a major end point.

Data from reported phase III trials of mCRPC were analyzed. The proportion of patients with measurable disease, setting (pre-docetaxel [D], D-based, post-D), year of starting accrual, PSA, and the requirement for symptoms were collected. The χ² test was used to evaluate the association of variables with measurable disease rate.

Twenty phase III trials totaling 19,276 men with mCRPC were evaluable. Three trials (n = 1289) started accruing before 2000 and 17 trials (n = 17,987) accrued after 2000. The proportion of measurable disease rate for all trials was 47.5%. The measurable disease rate was significantly higher (P < .001) in trials that accrued after 2000 versus before 2000 (48.7% vs. 31.1%; P < .001), D-based (51.8%) or post-D patients (48.9%) compared with pre-D patients (38.6%) and in trials allowing symptomatic versus asymptomatic/minimally symptomatic patients (50.1% vs. 40.0%).

The proportion of men with measurable disease was significantly higher in phase III trials of mCRPC that accrued after 2000, in D-based or post-D patients and in trials that allowed symptomatic patients. Because of the association of objective measurable changes with survival, Response Evaluation Criteria in Solid Tumors changes might warrant consideration as a major end point in phase II trials to obtain a firm signal of efficacy before launching phase III trials.