Abstract
<title>Abstract</title> <p>Purpose Positive surgical margins (PSM) after radical prostatectomy are associated with biochemical recurrence, although margin status reflects a combination of tumour-related, anatomical, and operative factors. We aimed to derive and internally validate an interpretable nomogram that accommodates non-linear predictor effects and estimates postoperative PSM probability after laparoscopic radical prostatectomy (LRP) or robot-assisted radical prostatectomy (RARP). Methods We retrospectively analysed 376 patients with prostate cancer who underwent LRP or RARP and had a documented postoperative margin status. The candidate set included demographic characteristics, indices of preoperative tumour burden, operative variables, comorbid conditions, and postoperative pathological findings. Least absolute shrinkage and selection operator (LASSO) regression was used for initial predictor reduction. Correlation matrices, variance inflation factors, and sensitivity analyses across Top-N predictor sets were used to examine redundancy, stability, and model size. Restricted cubic splines (RCS) were applied to continuous predictors to assess departures from linearity. The selected predictors were entered into multivariable logistic regression. Model performance was evaluated by receiver operating characteristic analysis, calibration plots, Brier scores, and decision curve analysis. Results PSM was identified in 155 of 376 patients (41.2%). Perineural invasion was associated with a higher probability of PSM (odds ratio [OR] 2.609, 95% confidence interval [CI] 1.328–5.124), as was the biopsy positive-core ratio (OR 1.020 per percentage point, 95% CI 1.005–1.035). The relation between preoperative log-transformed prostate-specific antigen and PSM appeared non-linear. The model yielded areas under the curve of 0.801 in the training cohort and 0.824 in the validation cohort; the corresponding Brier scores were 0.1778 and 0.1697. Conclusion The internally validated nomogram separated patients with and without PSM reasonably well, produced acceptably calibrated risk estimates, and may assist postoperative risk stratification after LRP or RARP. Independent validation is necessary before clinical implementation.</p>