Prediction of local failure by residual tumor cells after radical prostatectomy using retinoic acid receptor beta (RARB) promoter hypermethylation analysis

Background Positive surgical margins after radical prostatectomy (RP) are an imperfect surrogate of residual tumor and do not reliably identify men who will experience biochemical recurrence (BCR). Promoter hypermethylation of retinoic acid receptor beta gene ( RARB ) is a frequent epigenetic alteration in prostate cancer (PCa). We evaluated whether intraoperative sampling of the prostatic fossa with quantitative methylation-specific PCR (qMSP) for RARB improves prediction of BCR compared with conventional histology and margin status. Methods In a dual-centre study, 176 men with biopsy-proven PCa undergoing open or robot-assisted RP had nine standardized biopsies (sites A–I) taken from the prostatic fossa before vesicourethral anastomosis; 32 cystectomy patients served as cancer-free controls. Each fossa biopsy was split for routine histology and qMSP analysis of RARB ( MYOD1 as internal control). Clinicopathologic data and PSA follow-up were prospectively recorded. BCR was defined per German S3 guideline thresholds. Statistical testing included Pearson’s χ², Fisher’s exact, McNemar, and Mann–Whitney U tests (two-sided, α = 0.05). Results Median age was 65 years; median diagnostic PSA 7.15 ng/ml. On specimen assessment, 130 men were R0 and 46 R1. Among 164 fossa samples with benign histology, 96 (59%) were RARB -positive by qMSP; among 12 histologically malignant fossa samples, 9 (75%) were RARB -positive (Table 1). RARB hypermethylation associated significantly with surgical margin status (p < 0.0001) and with BCR (p = 0.039), but not with T-stage or initial PSA; associations by ISUP grade showed a trend for ≥ 3 (p = 0.090) and significance for ≥ 4 (p = 0.029). All 160 control-fossa samples were RARB -negative, while 20 prostate cancer tissue controls were RARB -positive. During a median 60-month follow-up (n = 152), 32 men (21%) developed BCR. In the BCR subset suitable for analysis (n = 27), fossa histology was positive in 3 (11%), specimen margin status was positive in 13 (48%), and RARB was positive in 23 (85%). For predicting BCR, RARB analysis outperformed margin status and fossa histology (each p < 0.001; McNemar where applicable). Conclusions Intraoperative prostatic fossa biopsies analyzed for RARB promoter hypermethylation detect molecular residual disease that is frequently missed by routine histology and provide superior prediction of BCR compared with surgical margin status. RARB methylation may enable earlier, biologically informed selection for adjuvant or early salvage radiotherapy while avoiding overtreatment in molecularly negative patients. Prospective validation and integration with multivariable models are warranted.