External validation of predictive models of sexual, urinary, bowel and hormonal function after surgery in prostate cancer subjects

Abstract

Background

In 2020, a research group published five linear longitudinal models, predict Expanded Prostate Cancer Index Composite-26 (EPIC-26) scores post-treatment for radical prostatectomy, external beam radiotherapy and active surveillance collectively in US patients with localized prostate cancer.

Methods

Our study externally validates the five prediction models for patient reported outcomes post-surgery for localised prostate cancer. The models’ calibration, fit, variance explained and discrimination (concordance-indices) were assessed. Two Australian validation cohorts 1 and 2 years post-prostatectomy were constructed, consisting of 669 and 439 subjects, respectively (750 in total). Patient reported function in five domains post-prostatectomy: sexual, bowel, hormonal, urinary incontinence and other urinary dysfunction (irritation/obstruction). Domain function was assessed using the EPIC-26 questionnaire.

Results

1 year post-surgery, R² was highest for the sexual domain (35%, SD = 0.02), lower for the bowel (21%, SD = 0.03) and hormone (15%, SD = 0.03) domains, and close to zero for urinary incontinence (1%, SD = 0.01) and irritation/obstruction (− 5%, SD = 0.04). Calibration slopes for these five models were 1.04 (SD = 0.04), 0.84 (SD = 0.06), 0.85 (SD = 0.06), 1.16 (SD = 0.13) and 0.45 (SD = 0.04), respectively. Calibration-in-the-large values were − 2.2 (SD = 0.6), 2.1 (SD = 0.01), 5.1 (SD = 0.1), 9.6 (SD = 0.9) and 4.0 (SD = 0.2), respectively. Concordance-indices were 0.73, 0.70, 0.70, 0.58 and 0.62, respectively (all had SD = 0.01). Mean absolute error and root mean square error were similar across the validation and development cohorts. The validation measures were largely similar at 2 years post-surgery.

Conclusions

The sexual, bowel and hormone domain models validated well and show promise for accurately predicting patient reported outcomes in a non-US surgical population. The urinary domain models validated poorly and may require recalibration or revision.