Proposal for an Expanded “R” Classification: Impact of Positive Surgical Margin Length on Biochemical Recurrence After Robotic Radical Prostatectomy

<b>Objectives</b>: In this study, the effect of positive surgical margin (PSM) length on predicting postoperative biochemical recurrence (BCR) after radical prostatectomy was evaluated, and based on the findings, an additional R subclassification to the TNM-R system was proposed. <b>Methods</b>: We retrospectively analyzed patients who underwent robot-assisted radical prostatectomy between 30 July 2008 and 31 December 2019. Only patients with PSM were included. Those with negative margins, those receiving neoadjuvant/adjuvant hormone therapy, or those with prior pelvic radiotherapy were excluded. A total of 353 pathology specimens were re-evaluated by a uropathologist, and the PSM length was quantitatively measured. BCR was defined as a PSA level of ≥0.2 ng/mL in two consecutive measurements. <b>Results</b>: The median follow-up time of the patients was 49.5 ± 33.4 months. BCR occurred in 27.1% (n = 96) of patients. A PSM cut-off length of 3.5 mm was identified for predicting BCR (<i>p</i> < 0.001). Among patients with PSM < 3.5 mm, 9.8% experienced BCR, while 54.3% of those with PSM ≥ 3.5 mm did. A PSM length ≥ 3.5 mm was associated with a higher risk of recurrence (OR: 1.249, 95% CI: 1.160-1.345, <i>p</i> < 0.001). In multivariate logistic regression analysis, PSM length remained an independent prognostic factor for BCR (<i>p</i> < 0.001). <b>Conclusions</b>: Quantitative measurement of PSM length serves as an independent predictor of BCR following radical prostatectomy. We propose subclassifying R1 margins into R1a (<3.5 mm) and R1b (≥3.5 mm), which may enhance prognostic accuracy in pathological reporting.