SUO 2017: A Quantitative Assessment Of Residual Confounding In The Comparison Between Surgery And Radiotherapy In The Treatment Of Non-Metastatic Prostate Cancer
Methods: The authors performed a population-based, retrospective cohort study of men treated for non-metastatic prostate cancer in Ontario, Canada from 2002-2009. Patients treated with surgery and radiotherapy were matched on demographics, comorbidity, and cardiovascular risk factors. The primary outcome was non-prostate cancer mortality. The Fine & Gray sub-distribution method with generalized estimating equations was used to compare outcomes. Additionally, the authors compared these patients with prostate cancer to the general population. The authors used a previously published technique to quantify the prevalence and strength of residual confounding necessary to account for observed results.
Results: The study demonstrated that of 20,651 eligible men, 10,786 (5393 pairs) were matched. The 10-year cumulative incidence of non-prostate cancer mortality was higher among patients who underwent radiotherapy (12%) than surgery (8%); adjusted sub-distribution hazard ratio 1.57, 95% CI 1.35-1.83). Both groups had significantly lower rates of non-prostate cancer mortality than matched men without prostate cancer (18%, p<0.001). Hypothetical residual confounders would have to be both strongly associated with non-prostate cancer mortality (HRs in excess of 2.5) and have highly differential prevalence in order to nullify the observed effect.
Conclusion: The authors concluded that patients treated for non-metastatic prostate cancer have significantly lower non-prostate cancer mortality than men in the general population. The authors identified the magnitude of potential residual confounders to account for differences in treatment effects for prostate cancer.
Presented by: Christopher Wallis, Toronto, Canada
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, @GoldbergHanan, at the 18th Annual Meeting of the Society of Urologic Oncology, November 29-December 1, 2017 – Washington, DC