PROK1 and prostate cancer: Although the PROK1 protein investigated in the present study was identified as an angiogenic factor in endocrine cells by Ferrara [21], the researchers observed its involvement in the hematogenous metastasis and autocrine mechanism-based invasive ability of human colorectal cancer cells, and its significance in various malignant tumors was demonstrated via its relationship with malignancy in prostate cancer, neuroblastoma, and pancreatic duct cancer [25–28].