Methylation Analysis of Four Genes in Negative Prostate Needle Biopsies Prior to Diagnosis of Cancer
M Amin, SH Merchant, AA Martinez, FA Vicini, SV Hunter, NS Goldstein. William Beaumont Hospital, Royal Oak, MI; VA Hospital, Albuquerque, NM; Advanced Diagnostic Lab, Redford, MI
Background: CpG island hypermethylation gene silencing is a characteristic feature of prostate adenocarcinoma (Pca). It is an early genetic event, being found in most Pcas and high grade PINs. Other groups have recommended gene sets sensitive to hypermethylation that can be used in Pca. A benign biopsy does not reliably exclude the presence of Pca in men with elevated PSA. This can produce a problematic clinical scenario, especially when played out over multiple benign biopsies. The goal of this study was to assess the effectiveness of a hypermethylation assay in benign prostate biopsies that preceded adenocarcinoma as a possible tool to identify the subset of high risk patients in whom saturation biopsies would be useful.
Design: DNA from 11 benign biopsies and 4 biopsies with high grade prostatic intraepithelial neoplasia (HGPIN) / atypical small acinar proliferation (ASAP) from patients with elevated PSAs that preceded Pca was extracted. The mean time interval between the initial benign/suspicious and malignant biopsies was 15.5 months (range 2.5-36 mos). Negative control cases were benign biopsies in patients who did not have subsequent Pca over a similar/longer time period. Positive controls were the subsequent Pcas. Genes assessed for hypermethylation were GSTP1, PTGS2, RASSF and APC. The MethylLight kit was used. Methylated and unmethylated primers were concurrently and separately assessed using Real time PCR.
Results: Hypermethylation was present in GSTP1, PTGS2, RASSF, and APC in 1/15, 12/15, 14/15, and 6/15 biopsies that preceded Pca, respectively. In the 11 benign biopsies preceding Pca, all four genes were hypermethylated in 1 case, three genes were hypermethylated in 2 cases, two genes were hypermethylated in 5 cases, and one gene was hypermethylated in 3 cases. In the 4 biopsies preceding Pca with ASAP/HGPIN, two cases had three genes and two had 2 genes hypermethylated. Subsequent Pcas had hypermethylation of all four genes in 100% cases.
Conclusions: Hypermethylation assay using genes previously shown to be sensitive to CpG island hypermethylation appears to be useful and sensitive adjunctive assay for patients with elevated PSA and negative biopsies to identify the subset at high risk for subsequent Pca. Given the global effect of hypermethylation, the presence of hypermethylated genes in benign tissue may occur by closely adjacent Pca or high grade PIN that escaped needle sampling.
Category: Genitourinary (including renal tumors)
Tuesday, March 10, 2009 9:15 AM
Platform Session: Section A, Tuesday Morning