Anti-Glutamate Receptor 2 as a New Potential Diagnostic Probe for Prostatic Adenocarcinoma: A Pilot Immunohistochemical Study

Diagnoses of prostatic carcinoma (PCa) have increased with widespread screening. While the use of α-methylacyl coA racemase (AMACR) and high-molecular-weight cytokeratins (HMCKs) have aided in distinguishing benign mimics from malignancy, their sensitivity and specificity are limited. We studied 6C4, a monoclonal antibody to glutamate receptor 2 (GluR2), an excitatory amino acid receptor subunit distributed throughout the central nervous system, on benign prostatic epithelium, high grade prostatic intra-epithelial neoplasia (HGPIN), and prostatic carcinoma. 10 cases with post-atrophic or adenosis-like prostate glands were also stained with PIN4 (Prostatic Intra-epithelial Neoplasia 4), an immunostain cocktail against AMACR, p63, and high molecular weight cytokeratin, in parallel with C64. Immunoreactivity for C64 was graded as negative (0-10%), +1 (11%-50%), and +2 (>50%). Malignant epithelium was classified by Gleason patterns. Gleason patterns 4 and 5 were subdivided into cribriform or non-cribriform type. Its utility in distinguishing post-atrophic or adenosis-like glands from prostate cancer, both of which show absence of basal cells on PIN4 immunostain, was also investigated. Our results revealed a statistically significant difference in staining of benign secretory prostatic epithelium, HGPIN, and low Gleason pattern carcinomas. The results also showed C64 is a sensitive marker in separating basal cell negative post-atrophic or adenosis-like glands from prostate carcinoma. Additionally, there was a statistically significant difference between staining of cribriform versus non-cribriform Gleason pattern 4 and 5 carcinomas. A limited number of lymph node metastases from cribriform and non-cribriform carcinomas were studied, and they stained the same as the primary tumor in the majority of cases. In conclusion, our preliminary data demonstrated potential diagnostic utility of C64 in the pathologic evaluation of prostatic carcinoma.