Localization of Macrophage Subtypes and Neutrophils in the Prostate Tumor Microenvironment and Their Association with Prostate Cancer Racial Disparities

Background: Black men are two to three times more likely to die from prostate cancer (PCa) than White men. This disparity is due in part to discrepancies in socioeconomic status and access to quality care. Studies also suggest that differences in the prevalence of innate immune cells and heightened function in the tumor microenvironment of Black men may promote PCa aggressiveness.

Methods: We evaluated the spatial localization of and quantified CD66ce neutrophils by immunohistochemistry and CD68 (pan), CD80 (M1), and CD163 (M2) macrophages by RNA in situ hybridization on formalin-fixed paraffin-embedded tissues from organ donor "normal" prostate (n = 9) and radical prostatectomy (n = 38) tissues from Black and White men. Neutrophils were quantified in PCa and matched benign tissues in tissue microarray (TMA) sets comprised of 560 White and 371 Black men. Likewise, macrophages were quantified in TMA sets comprised of tissues from 60 White and 120 Black men. The phosphatase and tensin homolog (PTEN) and ETS transcription factor ERG (ERG) expression status of each TMA PCa case was assessed via immunohistochemistry. Finally, neutrophils and macrophage subsets were assessed in a TMA set comprised of distant metastatic PCa tissues collected at autopsy (n = 6) sampled across multiple sites.

Results: CD66ce neutrophils were minimal in normal prostates, but were increased in PCa compared to benign tissues, in low grade compared to higher grade PCa, in PCa tissues from White compared to Black men, and in PCa with PTEN loss or ERG positivity. CD163 macrophages were the predominant macrophage subset in normal organ donor prostate tissues from both Black and White men and were significantly more abundant in organ donor compared to prostatectomy PCa tissues. CD68,  CD80, and CD163 macrophages were significantly increased in cancer compared to benign tissues and in cancers with ERG positivity. CD68 and CD163 macrophages were increased in higher grade cancers compared to low grade cancer and CD80 expression was significantly higher in benign prostatectomy tissues from Black compared to White men.

Conclusions: Innate immune cell infiltration is increased in the prostate tumor microenvironment of both Black and White men, however the composition of innate immune cell infiltration may vary between races.