Overall Survival in the Intervention Arm of a Randomized Controlled Screening Trial for Prostate Cancer Compared with a Clinically Diagnosed Cohort
Objectives: This population-based study provides comparisons of prostate cancer characteristics at diagnosis of two cohorts of men from two well-defined geographical areas exposed to different intensities of prostate cancer screening. Overall survival in both cohorts was compared with that in the general population. Methods: A cohort of 822 men randomized to the intervention arm of a prostate cancer screening trial and subsequently diagnosed with prostate cancer was compared with a nonrandomized cohort of 947 men who were clinically diagnosed with prostate cancer in a geographically neighboring region. In both cohorts, cases were diagnosed with prostate cancer between January 1989 and December 1997. A partitioning of overall survival by variables associated with cancer onset such as age at diagnosis, stage at diagnosis, and grade at diagnosis was performed. Results: Age at diagnosis, tumor extent at diagnosis, and grade at diagnosis were significantly different between the screened and clinically diagnosed cohort. The 5- and 10-yr survival rates were higher in the screened cohort than in the clinically diagnosed cohort (88.8% vs. 52.4%, and 68.4% vs. 29.6%, respectively). Significant differences in survival were evident for all age, stage, and grade subgroups, except for metastatic disease at diagnosis. Conclusions: Differences in overall survival favoring the screened population were observed for all baseline characteristics (age, stage, and grade of disease), and these variables may all explain differences in overall survival because screening achieves early diagnosis as well as a stage and grade shift. As observed survival rates in the screened population mirrored those within the general population, the contribution of lead time and overdiagnosis to final patient outcome is considered to be large as well.