[1068] Foamy Gland Carcinoma of the Prostate in Needle Biopsy: Incidence, Gleason Grade, and Comparative AMACR vs ERG Expression

Joshua I Warrick, Peter A Humphrey. University of Michigan, Ann Arbor, MI; Washington University, Saint Louis, MO

Background: Foamy gland carcinoma (FGC) is a variant pattern of prostatic acinar adenocarcinoma that may be deceptively benign-appearing, and has been shown to be a cause of missed carcinoma on prostate needle core biopsy (NCB). Also, immunohistochemical staining for AMACR is limited by a comparatively lower sensitivity for foamy gland carcinoma compared to usual acinar adenocarcinoma. FGC has not been characterized in a consecutive series of prostate NCBs, and it is not known if ERG immunohistochemistry provides added value beyond AMACR in detection of FGC. The purpose of this study was to characterize FGC on NCB, with focus on incidence, Gleason score, and expression of AMACR and ERG.
Design: 476 consecutive prostate cancer NCB cases were identified from our archives, diagnosed over a 2 year period. All cases were re-reviewed, and Gleason score was assigned using the modified ISUP/AFIP guidelines. Presence and extent of foamy gland carcinoma were quantified. Immunohistochemistry for AMACR and ERG was performed on a representative slide from each case. Slides stained with AMACR were evaluated for intensity (scored 0-3) and proportion of cells staining (scored 0-4). Intensity and proportion scores were added to give an overall score (maximum 7). ERG staining was scored as previously described.
Results: Of 476 consecutive prostate cancer diagnosed on NCB, 18% (85 cases) contained a FGC component. 7% (32 of 476) of all cases were pure FGC on NCB, representing 38% (32 of 85) of cases with a FGC component. Of the 85 cases identified, the following Gleason scores were assigned to the FGC component: 79% (67 cases) 3+3=6, 14% (12 cases) 3+4=7, 1% (1 case) 4+3=7, 4% (3 cases) 4+4=8, 1% (1 case) 4+5=9, and 1% (1 case) 5+3=8. 73 carcinomas with a FGC component had sufficient tissue for immunohistochemical studies. Of these, 90% (66 cases) were AMACR positive. Of the AMACR positive cases, 36% (24 of 66 cases) showed AMACR-low staining (sum score <6). 41% (30 cases) were ERG positive. None of the AMACR negative cases were ERG positive.
Conclusions: FCG is a common finding on prostate NCB, is usually found in association with usual acinar adenocarcinoma, and most commonly has Gleason score 6 on NCB. 90% of FGCs in our series were AMACR positive, indicating equivalent sensitivity to that seen in usual acinar adenocarcinoma, a finding different from that reported in the literature. ERG immunohistochemistry did not provide added diagnostic value beyond AMACR.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 78, Tuesday Morning


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