[1070] PSA and NKX3.1: A Comparative IHC Study of Sensitivity and Specificity in Prostate Cancer

Charlie Yu, David Tacha, Ryan Bremer, Thomas Haas. Biocare Medical, Concord, CA; Mercy Health Sytems, Janesville, WI

Background: Adenocarcinoma of the prostate can present as metastatic carcinoma, which typically can be confirmed in most metastatic sites by immunohistochemistry with PSA antibodies. A new anti-PSA rabbit monoclonal (RM) antibody has been developed, which theoretically combines the advantages of high affinity, due to its rabbit origin, and high specificity, resulting from its monoclonal nature. Additionally, NKX3.1 protein has recently been shown to be a superior and sensitive marker in the majority of primary and metastatic prostatic adenocarcinomas. This study compared the staining sensitivity of a mouse monoclonal PSA (M) cocktail, a new PSA (RM), and NKX3.1 rabbit polyclonal (P). The PSA (RM) was also tested for specificity in over 600 cases of various normal and neoplastic tissues.
Design: Formalin-fixed paraffin-embedded tissue microarrays (TMA) were deparaffinized in the usual manner, followed by antigen retrieval. PSA (M), PSA (RM) and NKX3.1 (P) were optimized for staining prostate cancers, using an HRP micro-polymer detection system and visualization with DAB.
Results: The PSA (RM) stained 163/167 (98%) cases of prostate cancer, including 94/94 cases with a Gleason score of 3 to 8, and 55/58 (95%) cases with a Gleason score of 9 or 10. All other cancers and normal tissues were 100% negative. Both PSA antibodies stained 67 of 70 (95%) cases and were negative in the same cases (Gleason score 9 and 10). A comparison of PSA (M) and NKX3.1 on 71 cases of prostate adenocarcinoma (Grade II-IV) is summarized in Table 1:

Table 1

Tumor Grade	PSA (M)	NKX3.1
II	21/22	21/22
III	26/27	26/27
IV	19/22	20/22

Conclusions: The newly developed PSA (RM) was 100% specific and demonstrated equivalent staining to PSA (M), but in some cases provided sharper staining. The NKX3.1 (P) was slightly superior to PSA (M) in grade IV tumors. The strong nuclear staining of NKX3.1 results in easier interpretation of low expression cases, compared to the cytoplasmic staining of PSA, which can be ambiguous in these cases. PSA (RM) and NKX3.1 may be suitable for differential diagnosis, work-ups of tumors of unknown origin and multiplex stains.
Category: Genitourinary (including renal tumors)

Wednesday, March 21, 2012 9:30 AM

Poster Session V # 122, Wednesday Morning