Objectives: To evaluate the impact of competing mortality and extended observation time on the cancer-related mortality in localized prostate cancer (PC).
Methods: A comparison was made between two theoretical populations of prostate cancer patients. Both populations had a slowly increasing mortality due to PC, corresponding to a 10-year cause-specific mortality of 15%. One population (A) experienced a high competing mortality reaching 50% after 10 years, corresponding to series on deferred treatment. The other population (B) experienced a low competing mortality, 10% after 10 years, corresponding to series on radical prostatectomy. The impact of these different competing mortality rates on the absolute number of patients succumbing to PC and the effect of extended follow-up to 15 years was assessed.
Results: The ultimate risk of death from PC after 10 years was 8% in group A and 12.3% in group B. When the observation time was extended to 15 years, group A had a 16.5% risk of cancer death and group B had a 35.3% risk. The PC mortality increased twofold between 10 and 15 years in group A (8% versus 16.5%) and threefold in group B (12.3% versus 35.3%).
Conclusions: Low cause-specific mortality rates at 10 years of follow-up in series on deferred treatment comprising older patients with high competing mortality cannot be extrapolated to younger patients with a low competing mortality. Long expected survival is associated with a considerable cancer-related mortality at 15 years (35%) despite favorable outcome at 10 years.