[794] Assessment of TMPRSS2: ERG (T:E) Gene Fusion in Prostatic Adenocarcinoma (CaP) by Fluorescence In Situ Hybridization (FISH) and Immunohistochemistry(IHC): Correlation of ERG Break-Apart and T:E Fusion Probes with ERG and TMPRSS2 Protein Expression

Melissa Bastacky, Marissa Gogniat, Carol Sherer, Kathleen Cieply, Aron Gedansky, Sheri Kavala, Anil Parwani, Rajiv Dhir, Marie Acquafondata, Franto Francis, Sheldon Bastacky. University of Pittsburgh, Pittsburgh, PA

Background: T:E gene fusion leading to transcription factor ERG protein overexpression occurs in many CaPs. T:E gene fusion can be assessed using ERG break-apart and T:E fusion probes. The aim of this study is to compare both probe methods, correlating results with ERG and TMPRSS2 protein expression.
Design: Formalin-fixed, paraffin-embedded tissue sections from 21 CaP pt samples (tissue microarray (n=10), needle bx (n=3), radical prostatectomy (n=8)) and control organ donor prostates (ODP; n=10) were obtained from the University of Pittsburgh tissue bank. Dual-color FISH (break-apart probe for ERG disruption, separate ERG and TMPRSS2 probes for T:E fusion) and immunohistochemistry (ERG (Biocare Medical) and TMPRSS2 (Epitomics)) were performed. FISH was positive if ≥ 20% of cells had ERG disruption or T:E fusion, with thresholds based on ODPs. IHC intensity (0-3) and distribution (0-100%) were scored. FISH and IHC results were correlated.
Results:

Comparison of FISH (ERG Disruption and T:E Fusion) and IHC (ERG and TMPRSS2) with Gleason Score

Gleason score	*ERG (FISH)	*T:E (FISH)	*ERG (IHC)	**TMPRSS2 (IHC)
3+3=6	3/4 (75%)	3/4 (75%)	4/4 (100%)	4/4 (100%)
3+4=7	4/7 (57%)	5/7 (71%)	4/7 (51%)	7/7 (100%)
4+3=7	3/5 (60%)	3/5 (60%)	2/5 (40%)	5/5 (100%)
4+4=8	2/5 (40%)	3/5 (60%)	2/5 (40%)	5/5 (100%)

*stains CaP only, **stains benign prostate glands and CaP

Correlation of FISH (ERG Break-Apart vs T:E fusion) with ERG - IHC

	FISH+/Total	ERG-IHC+/FISH+	ERG (mean intensity score of + cases)
ERG- break-apart (total)	15/21 (71%)	12/15 (80%)	2.1/3
- ERG-BT	9/21 (43%)	9/9 (100%)	3/3
- ERG-UBT	4/21 (19%)	2/4 (50%)	1/3
- ERG-BT+UBT	2/21 (9%)	1/2 (50%)	3/3
T:E fusion	15/21 (71%)	12/15 (80%)	2.1/3

ERG-BT (One normal chromosome and one ERG balanced translocation); ERG-UBT (ERG unbalanced translocation)


Conclusions: 1) ERG disruption and T:E fusion probes had similar concordance rates (80%) with ERG protein expression. 2) False positive ERG disruption occurred with unbalanced but not with balanced ERG translocation, suggesting that a BT preserves ERG gene function while an UBT may disrupt the gene. 3) False positive T:E fusion FISH may be due to a positional effect of chr 21 in the tissue section, causing an apparent juxtaposition of TMPRSS2 and ERG. 3) There was no correlation of CaP Gleason score with ERG gene disruption, T:E gene fusion, or ERG or TMPRSS2 protein expression. 4) ERG gene disruption, T:E gene fusion, and ERG (but not TMPRSS2) protein expression correlated with CaP.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 176, Monday Afternoon