Background: For localized prostate cancer (PCa), radical prostatectomy (RP) and radiotherapy (RT) are two standard interventions to decrease PCa mortality. Contemporary studies contained the elderly people, analyses focusing on patients over 75 years old were still lacking. Method: In the Surveillance Epidemiology and End Results (SEER) database (2004-2015), old people over 75-year-old with cT2 stage were selected in our research. Multivariable Cox proportional hazard models were used to analyze cancer-specific mortality (CSM) and overall mortality (OM) after adjustment. The propensity score matching was performed to assume the randomization. An instrument variate (IVA) was used to calculate the unmeasured confounders. Results: It showed that RP is superior to RT in OM and CSM after adjustment for covariates (hazard ratio [HR] = 0.54, 95% CI = 0.47-0.62, p<0.001 and HR = 0.30, 95% CI = 0.20-0.45, p<0.001, respectively). The cox model after matching indicated similar consequence (OM: HR = 0.53, 95% CI = 0.46-0.62, p<0.001; CSM: HR = 0.27, 95% CI = 0.17-0.43, p<0.001). In the IVA-adjusted model, the effect of treatment changed slightly (OM: HR = 0.65, 95% CI = 0.54-0.78, p<0.001; CSM: HR = 0.21, 95% CI = 0.12-0.37, p<0.001). Subgroup analyses showed a comparable benefit with various Gleason score (GS) and age. For patients with GS=7, those received RP obtained the highest risk decline for overall death (HR = 0.41, 95% CI = 0.32-0.52); and for patients with younger age, those received RP obtained the highest risk decline for CSM (HR = 0.11, 95% CI = 0.01-0.52). Conclusion: Patients over 75 years old with cT2 stage will obtain more benefit from RP compared with RT, especially for patients with GS=7 and younger age. Funding Statement: Supported by the National key research and development program of China (Grant No. SQ2017YFSF090096), the Prostate Cancer Foundation Young Investigator Award 2013, the National Natural Science Foundation of China (Grant No. 81300627, 81370855, 81702536, 81770756), Programs from Science and Technology Department of Sichuan Province (Grant No. 2014JY0219 and 2017HH0063) and Young Investigator Award of Sichuan University 2017. Declaration of Interests: The authors have no conflicts of interest to declare. Ethics Approval Statement: Missing
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