To test for cancer specific mortality (CSM) differences after either radical prostatectomy (RP) or radiotherapy (RT) in incidental prostate cancer (IPCa) patients.

Within the Surveillance, Epidemiology, and End Results (SEER) database (2004-2015), IPCa patients were identified. Cumulative incidence plots as well as competing risks regression (CRR) models were fitted to address CSM after adjustment for other-cause mortality (OCM). Furthermore, a subgroup analysis was performed to test for CSM differences between RP and RT according to Gleason sum (GS 6,7, and 8-10).

Of 1,466 IPCa patients, 770 (53%) underwent RP vs. 696 (47%) RT. Incidental PCa RT patients were older, and exhibited higher PSA, higher proportion of Gleason sum 8-10, and higher clinical T stage. In cumulative incidence plots, 5-year CSM rates adjusted for OCM were 0.9 for RP vs. 6.8% for RT (Δ = 5.9%). After multivariable adjustment for clinical characteristics (age, PSA, Gleason sum, and clinical T stage) as well as for OCM, RP was associated with a protective hazard ratio (HR) of 0.35 (95% confidence interval [CI] 0.15 - 0.78, p value = .01). Within Gleason sum 8-10 IPCA patients, RP was associated with a protective HR of 0.31 (P = .039).

Incidental PCa RT-treated patients exhibited less favorable clinical characteristics than their RP counterparts. Despite full adjustment, RP was associated with a protective effect relative to RT. This effect exclusively applied to the Gleason sum 8-10 subgroup. In consequence, IPCa patients harboring Gleason sum 8-10 should ideally be considered for RP instead of RT.