[962] ERG Immunohistochemical Staining Patterns as a Function of Prostate Cancer Distribution in Prostatic Evasive Anterior Tumours

Osman Mahamud, Karen Chadwick, Neil E Fleshner, Andrew J Evans. University Health Network, Toronto General Hospital, Toronto, ON, Canada; University Health Network, Princess Margaret Hospital, Toronto, ON, Canada

Background: Prostatic evasive anterior tumors (PEATS) is a clinical entity in prostate cancer (CaP) characterized by tumor in the anterior aspect of the gland that is difficult to diagnose by transrectal ultrasound guided (TRUS) biopsies. The usual clinical scenario is that of rising serum PSA with no or minimal CaP detected on serial TRUS biopsies and MRI scans that reveal large volume anterior disease. TMPRSS2-ERG gene fusions are found in approximately 50% of all CaP and positive immunohistochemical staining of CaP cells with ERG is a reliable surrogate for the presence of these rearrangements. The localization of tumors with respect to the TZ, peripheral zone (PZ) or fibromuscular zone (FMZ) and the ERG staining patterns of CaP in these zones have not been described in PEATS.
Design: Sixteen radical prostatectomy cases meeting the definition of PEATS were identified in our clinical database. In 15 cases (94%), all original H&E prostatectomy slides were available for review. The slides were reviewed to classify CaP location as being PZ, TZ or FMZ and to select sections for ERG staining. One or two sections from the anterior prostate with the largest CaP foci, chosen to represent PEATS areas, and one section (where possible) with a separate tumor focus in the posterolateral PZ were obtained for ERG analysis. The selected sections were stained with ERG and the tumor foci scored as being positive or negative. Representaive sections from three cases were also assessed by TMPRSS2-ERG break apart FISH to confirm the IHC findings.
Results: Anterior tumor foci were located predominantly in the TZ in 7/15 (48%) cases, FMZ in 4/15 (26%) or straddling the TZ and PZ in 4/15 (26%). No cases were found in which anterior tumor was predominantly in the PZ. Positive ERG staining occurred in 6/15 cases (40%) when all CaP foci were considered, with 4/6 (67%) positive foci being exclusively in the PZ. Only 1/6 (17%) ERG positive cases had positive staining in a TZ-predominant focus and 1/6 (17%) ERG positive cases had positive staining in a FMZ- predominant focus.
Conclusions: CaP in PEATS cases is predominantly located in the TZ and FMZ and is 2-fold less likely to show positive ERG staining than CaP in the posterolateral PZ, suggesting PEATS may represent a distinct subset of CaP in terms of molecular pathogenesis.
Category: Genitourinary (including renal tumors)

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 121, Wednesday Morning

 

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