Immunohistochemistry Ki-67 is a marker of cell proliferation. Using immunohistochemical markers can be helpful to determine and diagnose prostate intraepithelial neoplasia (PIN) and carcinoma prostate. There are many studies about Ki67 as a prognostic tool, a diagnostic tool, and a potential therapeutic target for cancer therapy, but there are no standard criteria to define the cut-off point for the value of Ki-67 in premalignant and malignant prostate lesions.