Effect of Prostate Cancer Severity on Functional Outcomes After Localized Treatment: Comparative Effectiveness Analysis of Surgery and Radiation Study Results.

BACKGROUND:Whether prostate cancer severity modifies patient-reported functional outcomes after radical prostatectomy (RP) or external beam radiotherapy (EBRT) for localized cancer is unknown. OBJECTIVE:The purpose of this study was to determine whether differences in predicted function over time between RP and EBRT varied by risk group. DESIGN, SETTING, AND PARTICIPANTS:The Comparative Effectiveness Analysis of Surgery and Radiation (CEASAR) study is a prospective, population-based, observational study that enrolled men with localized prostate cancer in 2011-2012. Among 2117 CEASAR participants who underwent RP or EBRT, 817 had low-risk, 902 intermediate-risk, and 398 high-risk disease. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS:Patient-reported, disease-specific function was measured using the 26-item Expanded Prostate Index Composite (at baseline and 6, 12, and 36 mo). Predicted function was estimated using regression models and compared by disease risk. RESULTS AND LIMITATIONS:Low-risk EBRT patients reported 3-yr sexual function scores 12 points higher than those of low-risk RP patients (RP, 39 points [95% confidence interval {CI}, 37-42] vs EBRT, 52 points [95% CI, 47-56]; p<0.001). The difference in 3-yr scores for high-risk patients was not clinically significant (RP, 32 points [95% CI, 28-35] vs EBRT, 38 points [95% CI, 33-42]; p=0.03). However, when using a commonly used binary definition of sexual function (erections firm enough for intercourse), no major differences were noted between RP and EBRT at 3 yr across low-, intermediate-, and high-risk disease strata. No clinically significant interactive effects between treatment and cancer severity were observed for incontinence, bowel, irritative voiding, and hormone domains. The primary limitation is the lack of firmly established thresholds for clinically significant differences in Expanded Prostate Index Composite domain scores. CONCLUSIONS:For men with low-risk prostate cancer, EBRT was associated w