PURPOSE:The optimal treatment of clinically localized prostate cancer is controversial. Most studies focus on biochemical (PSA) failure when comparing radical prostatectomy (RP) with radiation therapy (RT), but this endpoint has not been validated as predictive of overall survival (OS) or cause-specific survival (CSS). We analyzed the available literature to determine whether reliable conclusions could be made concerning the effectiveness of RP compared with RT with or without androgen deprivation therapy (ADT), assuming current treatment standards. METHODS:Articles published between February 29, 2004, and March 1, 2015, that compared OS and CSS after RP or RT with or without ADT were included. Because the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) system emphasis is on randomized controlled clinical trials, a reliability score (RS) was explored to further understand the issues associated with the study quality of observational studies, including appropriateness of treatment, source of data, clinical characteristics, and comorbidity. Lower RS values indicated lower reliability. RESULTS:Fourteen studies were identified, and 13 were completely evaluable. Thirteen of the 14 studies (93%) were observational studies with low-quality evidence. The median RS was 12 (range, 5-18); the median difference in 10-year OS and CSS favored RP over RT: 10% and 4%, respectively. In studies with a RS ≤12 (average RS 9) the 10-year OS and CSS median differences were 17% and 6%, respectively. For studies with a RS >12 (average RS 15.5), the 10-year OS and CSS median differences were 5.5% and 1%, respectively. Thus, we observed an association between low RS and a higher percentage difference in OS and CSS. CONCLUSIONS:Reliable evidence that RP provides a superior CSS to RT with ADT is lacking. The most reliable studies suggest that the differences in 10-year CSS between RP and RT are small, possibly <1%.