Interpretation of Domain Scores on the EPIC-How Does the Domain Score Translate into Functional Outcomes?

The EPIC-26 (Expanded Prostate Cancer Index Composite-Short Form) is a validated questionnaire for measuring health related quality of life. However, the relationship between domain scores and functional outcomes remains unclear, leading to potential confusion about expectations after treatment. For instance, does a sexual function domain score of 80 mean that a patient can achieve erection sufficient for intercourse? Consequently we sought to determine the relationship between the domain score and the response to obtaining the best possible outcome for each question.

Using data from the CEASAR (Comparative Effectiveness Analysis of Surgery and Radiation) study, a multicenter, prospective study of men diagnosed with localized prostate cancer, we analyzed 11,464 EPIC-26 questionnaires from a total of 2,563 men at baseline through 60 months of followup who were treated with robotic prostatectomy, radiotherapy or active surveillance. We dichotomized every item into its best possible outcome and assessed the percent of men at each domain score who achieved the best result.

For every EPIC-26 item the frequency of the best possible outcome was reported by domain score category. For example, a score of 80 to 100 on sexual function corresponded to 97% of men reporting erections sufficient for intercourse while at a score of 40 to 60 only 28% reported adequate erections. Also, at a score of 80 to 100 on the urinary incontinence domain 93% of men reported rarely or never leaking vs 6% at a score of 61 to 80.

Our findings indicate a novel way to interpret EPIC-26 domain scores, demonstrating large variations in the percent of respondents reporting the best possible outcomes over narrow domain score differences. This information may be valuable when counseling men on treatment options.