GSTP1 positive prostatic adenocarcinomas are more common in Black than White men in the United States

GSTP1 is a member of the Glutathione-S-transferase (GST) family silenced by CpG island DNA hypermethylation in 90-95% of prostate cancers. However, prostate cancers expressing GSTP1 have not been well characterized. We used immunohistochemistry against GSTP1 to examine 1673 primary prostatic adenocarcinomas on tissue microarrays (TMAs) with redundant sampling from the index tumor from prostatectomies. GSTP1 protein was positive in at least one TMA core in 7.7% of cases and in all TMA cores in 4.4% of cases. The percentage of adenocarcinomas from Black patients who had any GSTP1 positive TMA cores was 14.9%, which was 2.5 times higher than the percentage from White patients (5.9%; P < 0.001). Further, the percentages of tumors from Black patients who had all TMA spots positive for GSTP1 (9.5%) was 3-fold higher than the percentage from White patients (3.2%; P<0.001). In terms of association with other molecular alterations, GSTP1 positivity was enriched in ERG positive cancers among Black men. By in situ hybridization, GSTP1 mRNA expression was concordant with protein staining, supporting the lack of silencing of at least some GSTP1 alleles in GSTP1-positive tumor cells. This is the first report revealing that GSTP1-positive prostate cancers are substantially over-represented among prostate cancers from Black compared to White men. This observation should prompt additional studies to determine whether GSTP1 positive cases represent a distinct molecular subtype of prostate cancer and whether GSTP1 expression could provide a biological underpinning for the observed disparate outcomes for Black men.

Abstract 4582: Mannose receptor positive macrophage infiltrate correlates with prostate cancer onset and metastatic castration-resistant disease

M2-Tumor Associated macrophages (M2-TAMs) can suppress inflammation within the tumor microenvironment and have been reported to modulate cancer progression. We and others have previously reported infiltration of M2 macrophages in metastatic castrate-resistant prostate cancers (mCRPC). The objective of this study was to determine whether the extent of M2 macrophage infiltration correlates with prostate cancer aggressiveness, we applied immunohistochemistry to normal prostatic tissue, localized prostate cancer and metastatic castrate-resistant prostate cancer (mCRPC) from 192 patients. To assess M2 macrophage involvement, we analytically validated an IHC assay to detect the human mannose receptor (CD206). Also, we used multiplex immunofluorescent staining to show that a small fraction of CD206 staining co-localizes with endothelial cells of lymphatic vessels, while the vast majority of staining occurs in CD68-positive macrophages. The area fraction of staining for CD206-positive macrophages increased in a stepwise fashion going from normal (i.e. non-inflammation) prostatic tissue, to primary untreated carcinomas, to hormone naive regional lymph node metastases to castration resistant prostate cancer. Complimentary studies using flow cytometry confirmed CD206-positive M2-TAM infiltration. Altogether, this study revealed a progressive increase in CD206-positive macrophages from normal prostate to metastatic CRPC. Given the immunosuppressive nature of these cells and lack of clinical success of immunotherapy for prostate cancer patients, our results provide a rationale for therapeutic development to deplete these cells in the prostate cancer microenvironment as a potential method to augment immunotherapeutic approaches in prostate cancer.

Citation Format: Jelani C. Zarif, Javier A. Baena-Del Valle, Jessica L. Hicks, Christopher M. Heaphy, Igor Vidal, Jacob Luo, Tamara L. Lotan, Jody E. Hooper, William B. Isaacs, Kenneth J. Pienta, Angelo M. De Marzo. Mannose receptor positive macrophage infiltrate correlates with prostate cancer onset and metastatic castration-resistant disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4582.