[935] A Comparison of the Immunoexpression of ERG Versus AMACR, PSA and PSAP in Prostatic Carcinomas

Diana GS Lim, Ming Teh, Thomas P Thamboo. National University Health System, Singapore

Background: ERG overexpression secondary to TMPRSS2-ERG gene re-arrangement occurs in 40-70% of prostate carcinomas (PCs) and immunoexpression of ERG is reported to be a good surrogate for the detection of this fusion. We aimed to compare the immunoexpression of ERG and other commonly used immunomarkers, in a series of PCs.
Design: Tissue microarrays were constructed from 33 radical prostatectomy and 54 TURP specimens. A corresponding core of benign prostatic tissue was included when available. Expression of ERG, α-methyacyl-CoA racemase (AMACR), prostate specific antigen (PSA) and prostate specific acid phosphatase (PSAP) was evaluated using commercially available monoclonal antibodies. Intensity of staining was scored as negative (no staining), weak (1+), moderate (2+) and strong (3+) and extent of staining was scored as: 1+: ≥1% and <10%; 2+: ≥10% and <50%, 3+: ≥50% of cells showing immunoreactivity.
Results: 18/81(22.2%), 78/83 (94.0%), 75/84 (89.3%) and 82/84 (97.6%) PCs showed immunoreactivity for ERG, AMACR, PSAP and PSA respectively. Seven tumors expressing ERG showed weak staining, 8 showed moderate staining and 3 demonstrated strong immunoexpression. Seventeen tumors showed immunoreactivity for both ERG and AMACR (6 with Gleason score 6, 3 with Gleason score 7, 3 with Gleason score 8 and 5 with Gleason score 9). One tumor (Gleason score 9) showed strong and diffuse staining for ERG but only weak immunoexpression of PSA and did not stain for AMACR or PSAP. None of the cores of benign prostatic tissue stained for ERG (0/62), whereas 1/68, 70/70 and 71/71 cores of benign prostatic tissue showed immunoreactivity for AMACR, PSAP and PSA respectively.
Conclusions: ERG is a significantly less sensitive but only slightly more specific marker for PCs compared to AMACR. Incorporating ERG into a panel of immunomarkers that includes AMACR, for the detection of PCs, is of limited diagnostic utility. PSA and PSAP are very sensitive markers for indicating prostatic origin regardless of ERG status.
Category: Genitourinary (including renal tumors)

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 176, Wednesday Afternoon


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