KRT8 and prostate neoplasm: The end-stage PPR-RFP primary prostate tumors were poorly differentiated, with little or no glandular structure, and displayed strong coexpression of the luminal epithelial marker cytokeratin 8 (CK8) and the neuroendocrine marker synaptophysin (SYP), along with AR-negative tumors as their primary tumor components (Figure 5A).