GSTP1 CpG island hypermethylation for DNA-based detection of occult tumor cells in surgical margins after radical prostatectomy.

OBJECTIVE: The risk of local recurrence after radical prostatectomy (RP) is considerably dependent on local tumor stage. To improve local staging, the aim of this study was to assess the feasibility of quantitative methylation-specific PCR (Q-MSP) for the identification of promoter hypermethylation of the detoxifying glutathione-S-transferase P1 gene (GSTP1) to detect occult prostate cancer (PCa) cells in the prostatic fossa after RP.
METHODS: A total of 39 consecutive patients with clinically organ-confined PCa underwent RP. After gland excision, biopsies were obtained from eight defined areas of the prostatic fossa and bisected for both histopathological and molecular analyses. Results were related to clinicopathological data including tumor stage, Gleason score, prostate-specific antigen (PSA), and biochemical recurrence.
RESULTS: Of 39 patients, 11 with PCa had at least one positive molecular margin status indicated by GSTP1 methylation. These included 5 of 17 (29.4%) with organ-confined and 6 of 22 (27.3%) with advanced (≥pT3 and/or pN+) PCa. GSTP1 methylation in surgical margins strongly correlated with histopathological R-status (P = 0.022) and preoperative PSA (P = 0.01) whereas no association with tumor stage (pT2 vs pT3), grade (Gleason score <7 vs ≥7), and lymph node status was found. No patient experienced biochemical relapse.
CONCLUSIONS: GSTP1 hypermethylation detected by Q-MSP in prostatic fossa biopsies after RP is well suited for the detection of occult tumor cells in surgical margins. However, the limited number of patients and the short-term follow-up does not allow definite conclusions on the prognostic value of GSTP1 in surgical margins.