Vis A.¹, Roemeling S.¹, Reedijk A.², Otto S.³, Schroder F.¹

Presented on March, 22 2007

INTRODUCTION & 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. Furthermore, the overall survival in both cohorts was compared, whereas for both cohorts the overall survival was compared to that expected in the general population. Through this methodology of the expected survival, the magnitude of lead time and overdiagnosis of disease can be determined.

MATERIAL & 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 to a non-randomized cohort of 947 men whom 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 in both cohorts. The overall survival in both cohorts was compared to that in the general population.

RESULTS: The age at diagnosis, tumor extent at diagnosis, and grade at diagnosis were significantly different between the screened and clinically diagnosed cohort (P<.001). Five-and-ten year survival was higher in the screened cohort than in the clinically diagnosed cohort (88.8% versus 52.4%, and 68.4% versus 29.6%, respectively). Significant differences in survival were evident for all age-, stage-, and grade subgroups, except for metastatic disease-at-diagnosis. The expected survival in the screened cohort mirrored that in the expected population for all age-, grade-, and stage subgroups. The expected survival in the clinically diagnosed cohort was statistically significant lower than that expected in the general population.

CONCLUSIONS: Differences in survival favoring the screened population were observed for all baseline characteristics (age-, stage-, and grade-of-disease). These variables may all have influenced differences in survival rates to some extent, though it was not possible to determine the contribution of each individually. As the observed survival rates in the screened population mirrored those within the general population, the contribution of lead time and overdiagnosis of disease to final patient outcome is considered to be large.

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