Molecular Characterization of Gleason Pattern 3 Prostate Cancer with Co-Existing Adjacent Gleason Pattern 4 Cancer
Adam G Sowalsky, Huihui Ye, Steven P Balk. Beth Israel Deaconess Medical Center, Boston, MA
Background: Prostate cancer (PCa) often presents in multiple foci with different grades in the same individuals. It is unknown whether high grade PCa develops de novo or progresses from a lower grade tumor. The molecular features that determine different grades of PCa are not clear.
Design: Using 19 radical prostatectomy specimens of multifocal PCa that contain immediately adjacent G3 and G4 foci, we assessed whether adjacent G3/G4 foci share a common clonality through examining their 1) TMPRSS2-ERG fusion status, by screening 19 cases for ERG expression using immunohistochemistry and confirming fusion mRNA using qRT-PCR in 6 ERG-positive cases, 2) TMPRSS2 and ERG genomic breakpoints using hybrid capture and sequencing of genomic DNA in 6 fusion positive cases, and 3) RNA expression profiles using Affymetrix ExonST arrays in 6 cases. Laser-capture microdissection was used to purify cancerous glands for genetic assays in this study.
Results: 1) All 19 cases of PCa with adjacent G3/G4 foci showed a concordant ERG expression pattern, regardless whether the adjacent G3/G4 foci were separated (n=16) or intermixed (n=3). 9 cases were concordantly positive for ERG expression with equal immunointensity, except in one case that the G3 focus showed a lower ERG immunointensity than the adjacent G4 focus. 10 cases were concordantly negative for ERG expression. ERG positive rate was 47% (9/19), which is in agreement with the reported frequency in the literature. We examined TMPRSS2-ERG fusion using qRT-PCR in 6 ERG-positive cases, which were all positive for TMPRSS2-ERG mRNA expression; 2) TMPRSS2 and ERG breakpoints have been shown to be random in a ∼ 25-kb region between exon 1 and exon 4 of TMPRSS2 and ∼75-kb region in intron 3 of ERG. We have submitted hybrid-captured TMPRSS2 and ERG genomic DNA for breakpoint sequencing in 6 fusion positive cases. The sequencing results will be soon available, which will further validate the clonality; 3) ExonST arrays showed remarkably similar RNA expression profiles in adjacent G3/G4 foci in all 6 cases examined. A few genes showed a significant difference in expression levels in adjacent G3/G4 foci.
Conclusions: In cases of multifocal PCa, adjacent G3/G4 foci are much more likely to share the same clonal origin than to be two independent clones. Additional studies need to be done to identify molecular signatures to distinguish G4-associated G3 PCa from indolent G3 PCa.
Category: Genitourinary (including renal tumors)
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 107, Tuesday Afternoon