[920] FAS-N Expression in Prostate Cancer: Can It Be Used To Distinguish Cancer from Benign in Prostate Biopsies?

J Zhang, G Msangi, S Bryant, E Ryu, T Sebo. Mayo Clinic, Rochester, MN

Background: Fatty acid synthase (FAS) is a cytosolic polypeptide that is required for de novo lipogenesis. FAS has been found to be over expressed in different cancers, including prostate cancer. Further studies have shown that FAS over expression occurs early in the development of prostate cancer. However, its expression in detecting prostate cancer in prostate core biopsy with the hope of using it as a new modality to diagnose prostate cancer has not been fully investigated, especially where H & E staining is limited.
Design: A total of 121 cases identified from the years 2000 to 2006 with prostate core biopsy tissue containing adenocarcinoma and confirmed at prostatectomy with a Gleason score (GS) of 6 or greater were retrieved from Division of Anatomic Pathology and immunohistochemically stained for FAS-N using a monoclonal antibody from DAKO, Carpenteria, CA. The stains were independently evaluated by three observers and a case was considered negative (0) if <1% of the cells of interest exhibited immunoreactivity. Positive stains were graded as weak (1+), intermediate (2+) or strong (3+); as well as focal if 1-50% of the cells stained or diffuse if >50% of the cells stained.
Results: We had a total of 121 patients whose ages ranged from 43 to 88yrs with a median of 68yrs. Patients cancer ranged from GS of 6 to 10 with a median of GS 8. Approximately 27% of the sample had GS 6. In each of the GS 7, 8 and 9 there was 21% of the sample. 8% had GS 10. Table 1 shows frequency for each of the 4 staining levels. Atrophic tissue stains the least with 99% of it showing no staining at all. The majority (75%) show no staining. On the reverse side, most cancers show either 3+ (44%), 2+ (27%) or 1+ (28%), only 1 case had no staining. High grade PINs mostly (55.4%) show no staining.

Table 1: Frequency table (with percentages) for each staining intensity

Intensity	0	1+	2+	3+
Atrophy	120 (99.2%)	1 (0.8%)	0 (0.0%)	0 (0.0%)
Benign	91 (75.2%)	30 (24.8%)	0 (0.0%)	0 (0.0%)
Adenocarcinoma	1 (0.8%)	34 (28.1%)	33 (27.3%)	53 (43.8%)
Hg PIN	67 (55.4%)	18 (14.9%)	24 (19.8%)	12 (9.9%)

Conclusions: FAS-N can be used to distinguish adenocarcinoma from benign including atrophic prostate tissue in biopsy with high sensitivity (99%) and specificity (100%) when the staining intensity is 2+ or 3+. When the staining intensity is weak (1+) or the differential diagnosis is an Hg PIN, a routine basal cell layer marker should be added to aid in diagnosis.
Category: Genitourinary (including renal tumors)

Tuesday, March 10, 2009 11:45 AM

Platform Session: Section A, Tuesday Morning