[787] "More Cocktails, More Cancer"; Do Pathologists Who Use Immunohistochemistry More Frequently on Prostate Biopsies, Diagnose Prostate Cancer More Frequently?

Sameer Al Diffalha, Woodlyne Roquiz, Guliz A Barkan, Eva M Wojcik, Maria M Picken, Stefan E Pambuccian. Loyola University Chicago, Maywood, IL

Background: Atypical small acinar proliferations (ASAP), found in 1.5-5% of all prostate biopsies, are very small foci of atypical glands (usually <10 glands and <0.5 mm), which show no definite histologic features of malignancy and cannot be reproducibly classified as benign or malignant based on routine histology. Immunohistochemical (IHC) stains for basal cells (p63, HMWCK) and alpha-Methylacyl-CoA Racemase (AMACR), ideally combined into a cocktail, can be helpful in ASAP to differentiate prostate carcinoma (PC) from its benign mimics. The aim of this study was to determine the pathologists' frequency of use of IHC stains to resolve ASAP in routine practice, and the impact of IHC use on their diagnostic rates of PC and ASAP.
Design: We performed a retrospective review of all prostatic needle biopsies diagnosed from 1/1/2006 to 9/20/2012, recording data on the sign-out pathologist, diagnosis, and use IHC (p63/34βE12/AMACR cocktail) for each individually labeled biopsy site, which was considered a biopsy unit (BU). Each pathologist's % IHC use, % ASAP and % PC diagnosis was calculated. Comparisons between groups were made using χ2 or Fisher's exact test. p<0.05 was considered significant.
Results: During the study period, 12510 BU (each composed of 1-3 cores) from 2085 men were diagnosed by 12 pathologists (average 1043, range 270-3282 per pathologist). IHC was used in an average 2.5% of BU (range 0-7%). ASAP was diagnosed in 1.7% (range 0-4.6%) and PC in 14.6% (range 6.6-17.5%) of BU. 5 pathologists who used IHC ≥1% were defined as "high users" (HU) and 7 pathologists who used IHC <1% as "low users" (LU). The HU diagnosed more BU (8112 vs. 4398) and had a higher % PC (15.47% vs. 12.96%, p<0.0001), a higher % PC diagnosed after IHC (78/1255, 6.2% vs. 2/570, 0.4%, p<0.0001), a narrower range of variation of %PC (13.96%-17.51% vs. 6.60 -16.93 %) and a higher %ASAP (2.4% vs. 0.3%, p<0.0001) than LU. Overall IHC "resolved" ASAP to either benign or malignant in 42.7% (individual pathologists' range 0-90%, HU mean 43.37%, LU mean 25%).
Conclusions: Our results suggest that pathologists have different thresholds for regarding a focus as atypical, have different IHC ordering behavior, and may use IHC differently (i.e. some to confirm PC, others to rule it out). Pathologists who use IHC more frequently, diagnose PC more frequently and have less variation in the frequency of PC diagnoses than pathologists who use IHC less frequently. These results suggest the need for more explicit guidelines for the use and interpretation of IHC in ASAP.
Category: Genitourinary (including renal tumors)

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 125, Monday Morning


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