Lymph node ratio determines the benefit of adjuvant radiotherapy in pathologically 3 or less lymph node-positive prostate cancer after radical prostatectomy: a population-based analysis with propensity-score matching.

Background: The survival benefit of adjuvant radiotherapy (ART) in prostate adenocarcinoma, with limited numbers of pathologically involved lymph nodes (LNs) after radical prostatectomy (RP), is controversial.

Materials and Methods: From 2004 to 2014, data for prostate cancer patients categorized as N1M0 after RP were retrieved from the Surveillance, Epidemiology, and End Results (SEER) database. After propensity-score matching, the 10-year cancer-specific survival (CSS) rates between patients who received ART (ART group) or did not/unknown (no-ART group) were compared for each stratum of lymph node ratio (LNR) (%) according to the number of involved LNs.

Results: Optimal matching formed pairs of no-ART ( n = 905) and ART ( n = 905) groups. ART increased the CSS rate, even in patients with up to 3 positive LNs when the LNR is 7% or higher.

Conclusions: ART after RP showed a CSS benefit in prostate adenocarcinoma with 4 or more involved LNs irrespective of LNR. In prostate adenocarcinoma with up to 3 involved LNs after RP, ART may provide CSS benefits when the LNR is 7% or higher. The number of LN dissections required to achieve an LNR below 7% is 15, 29, and 43 or more for 1, 2, and 3 involved LNs, respectively.