Objectives: To assess the feasibility of methylation-specific PCR (MSP) for the detection of promoter hypermethylation of the detoxifying glutathione-S-transferase P1 gene (GSTP1) to detect occult prostate cancer cells in lymph nodes (LNs).
Methods: Paraffin-embedded pelvic LNs from 20 patients with pT2pN0M0R0 prostate cancer who developed PSA relapse were assessed by MSP. In 18 of the patients, samples of the primary tumor were obtained for MSP. In 19 patients, bone marrow (BM) aspirates were analyzed preoperatively for disseminated tumor cells by immunocytochemistry (mAb A45-B/B3). In 16 patients, biopsies of the anastomotic region were performed following PSA relapse. As a negative control GSTP1 methylation status was also assessed in LNs from 9 patients for whom an autopsy was performed for non-cancer-related causes.
Results: All primary tumors displayed GSTP1 hypermethylation (HM). Preoperative BM assessment showed disseminated tumor cells in 8/20 cases (40%). In 4 patients, biopsies of the vesico-urethral anastomosis showed local tumor recurrence. The LNs in the cancer patients showed GSTP1 HM in 18/20 cases (90%) versus 1/9 patients (11.1%) in the non-cancer cohort (p<0.0001).
Conclusion: GSTP1 HM appears to be well suited for molecular staging of prostate cancer and accurately detects disseminated tumor cells in LNs, which was seen in 90% of the patients with PSA relapse. However, the limited number of patients and the finding of benign and malignant prostatic tissue at the vesico-urethral anastomosis as a putative local source of PSA recurrence does not allow us to draw conclusions on the prognostic significance of our findings, yet.